CINXE.COM

<html> <head><script type="text/javascript" src="https://web-static.archive.org/_static/js/bundle-playback.js?v=7YQSqjSh" charset="utf-8"></script> <script type="text/javascript" src="https://web-static.archive.org/_static/js/wombat.js?v=txqj7nKC" charset="utf-8"></script> <script>window.RufflePlayer=window.RufflePlayer||{};window.RufflePlayer.config={"autoplay":"on","unmuteOverlay":"hidden"};</script> <script type="text/javascript" src="https://web-static.archive.org/_static/js/ruffle/ruffle.js"></script> <script type="text/javascript"> __wm.init("https://web.archive.org/web"); __wm.wombat("https://www.bipm.org/en/measurement-units/","20200524105425","https://web.archive.org/","web","https://web-static.archive.org/_static/", "1590317665"); </script> <link rel="stylesheet" type="text/css" href="https://web-static.archive.org/_static/css/banner-styles.css?v=p7PEIJWi" /> <link rel="stylesheet" type="text/css" href="https://web-static.archive.org/_static/css/iconochive.css?v=3PDvdIFv" />  <meta http-equiv="X-UA-Compatible" content="IE=8"/> <title>BIPM - measurement units</title> <meta name="description" content="The International System of Units (SI)"> <script language="javascript" src="/web/20200524105425js_/https://www.bipm.org/utils/onLoad.js"> </script> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//web.archive.org/web/20200524105425/https://www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-38070491-1', 'auto'); ga('send', 'pageview'); </script> <script src="/web/20200524105425js_/https://www.bipm.org/utils/jquery/jquery-1.10.2.min.js"></script> <script src="/web/20200524105425js_/https://www.bipm.org/utils/jquery/jquery-ui-1.10.3.custom/js/jquery-ui-1.10.3.custom.js"></script> <script src="/web/20200524105425js_/https://www.bipm.org/utils/zee/unslider.min.js"></script> <script src="/web/20200524105425js_/https://www.bipm.org/utils/zee/slider.js"></script> <script src="/web/20200524105425js_/https://www.bipm.org/utils/zee/cookie.js"></script> <link rel="stylesheet" href="/web/20200524105425cs_/https://www.bipm.org/utils/jquery/jquery-ui-1.10.3.custom/css/smoothness/jquery-ui-1.10.3.custom.css"> <link rel="stylesheet" href="/web/20200524105425cs_/https://www.bipm.org/resources/demos/style.css"> <link rel="stylesheet" href="/web/20200524105425cs_/https://www.bipm.org/utils/typoZEE.css" type="text/css"> </head> <body bgcolor="#FFFFFF" leftmargin="0" rightmargin="0" topmargin="0" marginwidth="0" marginheight="0"> <script> $(function() { $( "#tabs" ).tabs(); }); </script>  <a name="haut">  <center> <table width="1000" cellspacing="0" cellpadding="2" border="0"> <tr> <td width="10"></td><td width="180"></td><td width="530"></td><td width="270"></td><td width="10"></td></tr> <tr height="90"> <td width="10"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="90"></td> <td width="180" valign="center" align="left"><a href="/web/20200524105425/https://www.bipm.org/en/about-us/" title="BIPM home page"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/logoBIPM-RB.jpg" border="0"></a></td> <td width="530" valign="center" align="center" class="intro">    the intergovernmental organization through which Member States act together<br>      on matters related to measurement science and measurement standards.</td> <td width="270" align="center" valign="top"> <script language="javascript"> function ActionForm(f) { f.q.style.background = "white"; } </script> <form name="search" action="https://web.archive.org/web/20200524105425/https://search.bipm.org/bipm/en/C="> <table width="180" align="right" valign="top" border="0"> <tr height="50"> <td valign="bottom" class="intro">Search facility: <input onclick="ActionForm(this.form)" style="vertical-align: middle;background-image:url(/web/20200524105425im_/https://www.bipm.org/utils/en/img/bipm_portal.gif); background-repeat:no-repeat; background-position:center right;" type="text" name="q" size="25" maxlength="50"> <input type="hidden" name="action" value="s"> <input type="hidden" name="setcontext" value=""> </td> <td height="25" colspan="2" width="50" valign="bottom" align="left"><input type="image" src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/exalead.gif" border="0"></td> </tr> </table> </form> <br> <br> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="270" height="15" border="0"> <nobr><a href="/web/20200524105425/https://www.bipm.org/en/about-us/"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/home.png" border="0"></a> | <a class="navigation" href="/web/20200524105425/https://www.bipm.org/en/about-us/map.html">Site map</a> | <a class="navigation" href="/web/20200524105425/https://www.bipm.org/en/news/">News</a> | <a class="navigation" href="javascript:hidden_email('webmaster','bipm.org','BIPM website');">Contact us</a> | [<a id="langChange" data-lang="fr" href="/web/20200524105425/https://www.bipm.org/fr/measurement-units/" class="GrosTitreVO"> FR </a>] </nobr> </td> <td width="10"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="90"></td> </tr> </table>   <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td nowrap width="100%"> <style media="all" type="text/css"></style> <div class="menu"> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/about-us/" target="_self">  About us</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/about-us/role.html" target="_self">Our role and objectives</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/about-us/governance/" target="_self">Governance</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/about-us/member-states/" target="_self">Member States</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/about-us/associates/" target="_self">Associates</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/" target="_self">International System of Units (SI)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/" target="_self">International equivalence of measurements<br>(CIPM MRA)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/" target="_self">Our committees</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/" target="_self">Our work programme</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/sections/" target="_self">The BIPM staff</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/vacancies/" target="_self">Jobs and Secondments</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/procurement/" target="_self">Procurement and Sales</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/directions/" target="_self">How to get to the BIPM</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/about-us/pavillon-de-breteuil/" target="_self">History of the Pavillon de Breteuil</a></li> </ul> </li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/" target="_self"> Worldwide metrology</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/" target="_self">What is metrology?</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/" target="_self">International equivalence of measurements<br>(CIPM MRA)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/metre-convention/" target="_self">The Metre Convention</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/cgpm/" target="_self">The General Conference (CGPM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cipm/" target="_self">The International Committee (CIPM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/" target="_self">CIPM Consultative Committees (CCs)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/national/" target="_self">National Metrology Institutes (NMIs)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/regional/" target="_self">Regional Metrology Organizations (RMOs)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/jc/" target="_self">Joint Committees</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/liaisons/" target="_self">BIPM liaison work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cbkt/" target="_self">BIPM Capacity Building & Knowledge Transfer Programme</a></li> <li><a href="https://web.archive.org/web/20200524105425/http://www.worldmetrologyday.org/" target="_blank">World Metrology Day</a></li> </ul> </li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/" target="_self"> International equivalence</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/" target="_self">What is the CIPM MRA?</a></li> <li><a href="https://web.archive.org/web/20200524105425/https://www.bipm.org/kcdb" target="_self">CIPM MRA database <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img2/logo_kcdb_pt.gif"></a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/participation/" target="_self">Participating laboratories</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/cipm-mra-documents/" target="_self">CIPM MRA documents</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/approval-process.html" target="_self">CMC approval process</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cipm-mra/logo/" target="_self">Use of the CIPM MRA logo</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/jc/jcrb/" target="_self">JCRB: Joint Committee of the RMOs and the BIPM</a></li> </ul> </li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/" target="_self"> SI units</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/" target="_self">The International System of Units (SI)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/appendix1.html" target="_self">Decisions of the CGPM and the CIPM</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/mises-en-pratique/" target="_self">How to realize the definitions in practice</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/base-units.html" target="_self">Unit definitions</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/prefixes.html" target="_self">SI prefixes</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/si-download-area/" target="_self">Revised SI: Download area</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/history-si/" target="_self">Brief history of the SI</a></li> </ul> </li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/" target="_self"> Services</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/comparisons/" target="_self">Comparisons piloted by the BIPM</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/calibrations/" target="_self">Calibration and measurement services</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/tai/" target="_self">Timescales</a></li> <li><a href="https://web.archive.org/web/20200524105425/https://www.bipm.org/kcdb" target="_self"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img2/logo_kcdb_pt.gif" alt="KCDB" vspace="2"></a></li> <li><a href="https://web.archive.org/web/20200524105425/https://www.bipm.org/jctlm/" target="_self"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img2/logo_jctlm_pt.gif" alt="JCTLM" vspace="2"></a></li> <li><a href="https://web.archive.org/web/20200524105425/http://imrr.bipm.org/" target="_self"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img2/logo_imrr_pt.gif" alt="IMRR" vspace="2"></a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="https://web.archive.org/web/20200524105425/http://iopscience.iop.org/0026-1394/" target="metrologia"><i>Metrologia</i></a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/" target="_self">Meetings</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies.html" target="_self">Recommended values of standard frequencies</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/ionizing/radionuclides/sir/" target="_self">International Reference System (SIR)</a></li> </ul> </li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/" target="_self"> Publications</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/mises-en-pratique/" target="_self"><i>Mises en pratique</i></a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/directors-report/" target="_self">Annual Director's Report</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cipm/publications-cipm.html#ra" target="_self">Financial Report</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cipm/publications-cipm.html#no" target="_self">Notification of Contributions</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/" target="_self">Official proceedings</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/cgpm/resolutions.html" target="_self">Resolutions of the General Conference</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/open-literature/" target="_self">Scientific output</a></li> <li><a href="https://web.archive.org/web/20200524105425/http://iopscience.iop.org/0026-1394/" target="metrologia"><i>Metrologia</i></a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/guides/" target="_self">Guides in Metrology</a></li> </ul> </li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/diary/" target="_self"> Meetings</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/diary/" target="_self">List of meetings</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/" target="_self">BIPM Conference Centre</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/directions/" target="_self">How to get to the BIPM</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/cgpm-2018/" target="_self">General Conference (CGPM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cipm/" target="_self">International Committee (CIPM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/" target="_self">Consultative Committees and Working Groups</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/bipm-workshops/" target="_self">BIPM Workshops</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/other-events/" target="_self">Other BIPM events</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/" target="_self">Meeting reports</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/metrology-events.html" target="_self">External events</a></li> </ul> </li> </ul> </div> </td> </tr> </table>   <center> <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td width="10" height="50"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="50"></td> <td align="left" width="100%" height="50" background="/web/20200524105425im_/https://www.bipm.org/utils/common/img/cadre_trait.gif"> <table width="100%" border="0" background="/web/20200524105425im_/https://www.bipm.org/en/measurement-units/"> <tr> <td align="left" class="GrosTitre"><div name="exalead-titre">The International System of Units (SI)</div></td> </tr> </table> </td> <td width="10" height="50"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="50"></td> </tr> </table> </center>   <center><table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td width="10"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> <td valign="top" width="100%" class="txt12pt">  <div id="tabs"> <ul> <li><a href="#introduction">Introduction</a></li> <li><a href="#si-definition">Definition of the SI</a></li> <li><a href="#si-base-units">SI base units</a></li> <li><a href="#si-prefixes">SI prefixes</a></li> <li><a href="#cgpm-2018">The 2018 revision of the SI</a></li> <li><a href="#si-en-pratique"><a href="/web/20200524105425/https://www.bipm.org/en/publications/mises-en-pratique/">How to realize the SI units <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet6.gif" border="0"></a></a></li> <li><a href="#si-brochure"><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/">SI Brochure <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet6.gif" border="0"></a></a></li> <li><a href="#si-history"><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/history-si/">History <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet6.gif" border="0"></a></a></li> </ul> <div id="introduction" class="txt12pt"> <ul> <p><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14"> The recommended practical system of units of measurement is the International System of Units (<i>Système International d'Unités</i>), with the international abbreviation <b>SI</b>.</p> <table align="left" cellpadding="15" border="0"><tr><td> <a href="/web/20200524105425/https://www.bipm.org/en/si-download-area/"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-7.jpg" width="300" height="300" border="0"></a></td></tr></table> <p>The SI is defined by the <a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" class="introGras"><b>SI Brochure</b></a>, which is published by the BIPM.</p> <p>In a landmark decision, Member States voted on 16 November 2018 to revise the SI, changing the world's definition of the kilogram, the ampere, the kelvin and the mole.</p> <p>This decision, made at the 26th meeting of the General Conference on Weights and Measures (CGPM), means that from 20 May 2019 all SI units are defined in terms of constants that describe the natural world. This will assure the future stability of the SI and open the opportunity for the use of new technologies, including quantum technologies, to implement the definitions.</p> <p>The seven defining constants of the SI are:</p> <table border="0"><tr><td width="20"></td><td> <ul> <li>the caesium hyperfine frequency <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub>;</li> <li>the speed of light in vacuum <i>c</i>;</li> <li>the Planck constant <i>h</i>;</li> <li>the elementary charge <i>e</i>;</li> <li>the Boltzmann constant <i>k</i>;</li> <li>the Avogadro constant <i>N</i><sub>A</sub>; and</li> <li>the luminous efficacy of a defined visible radiation <i>K</i><sub>cd</sub>.</li> </ul> </td></tr></table> <p>The SI was previously defined in terms of seven base units and derived units defined as products of powers of the base units. The seven base units were chosen for historical reasons, and were, by convention, regarded as dimensionally independent: the metre, the kilogram, the second, the ampere, the kelvin, the mole, and the candela. This role for the base units continues in the present SI even though the SI itself is now defined in terms of the defining constants above.</p> </ul> </div> <div id="si-definition" class="txt12pt"> <ul> <p><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">The definition of the SI units is established in terms of a set of seven defining constants. The complete system of units can be derived from the fixed values of these defining constants, expressed in the units of the SI. These seven defining constants are the most fundamental feature of the definition of the entire system of units.</p> <table align="right" border="0"><tr><td width="15"><td> <a href="/web/20200524105425/https://www.bipm.org/en/si-download/"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-7.jpg" width="250" height="250" border="0"></a></td></tr></table> <p><b>The seven defining constants of the SI and the seven corresponding units they define:</b></p> <table align="left" border="0"> <tr height="1" bgcolor="#829EBA"><td colspan="4"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td></tr> <tr><td class="txt11ptlg" width="240">Defining constant</td> <td class="txt11ptlg" width="70">Symbol</td> <td class="txt11ptlg" width="200">Numerical value</td> <td class="txt11ptlg" width="50">Unit</td> </tr> <tr height="1" bgcolor="#829EBA"><td colspan="4"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td></tr> <tr><td class="txt11ptl">hyperfine transition frequency of Cs</td> <td class="txt11ptl"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/nu.gif" alt="nu"><sub>Cs</sub></td> <td class="txt11ptl">9 192 631 770</td> <td class="txt11ptl">Hz</td> </tr> <tr><td class="txt11ptl">speed of light in vacuum</td> <td class="txt11ptl"><i>c</i></td> <td class="txt11ptl">299 792 458</td> <td class="txt11ptl">m s<sup>1</sup></td> </tr> <tr><td class="txt11ptl">Planck constant</td> <td class="txt11ptl"><i>h</i></td> <td class="txt11ptl">6.626 070 15 x 10<sup>34</sup></td> <td class="txt11ptl">J s</td> </tr> <tr><td class="txt11ptl">elementary charge</td> <td class="txt11ptl"><i>e</i></td> <td class="txt11ptl">1.602 176 634 x 10<sup>19</sup></td> <td class="txt11ptl">C</td> </tr> <tr><td class="txt11ptl">Boltzmann constant</td> <td class="txt11ptl"><i>k</i></td> <td class="txt11ptl">1.380 649 x 10<sup>23</sup></td> <td class="txt11ptl">J K<sup>1</sup></td> </tr> <tr><td class="txt11ptl">Avogadro constant</td> <td class="txt11ptl"><i>N</i><sub>A</sub></td> <td class="txt11ptl">6.022 140 76 x 10<sup>23</sup></td> <td class="txt11ptl">mol<sup>1</sup></td> </tr> <tr><td class="txt11ptl">luminous efficacy</td> <td class="txt11ptl"><i>K</i><sub>cd</sub></td> <td class="txt11ptl">683</td> <td class="txt11ptl">lm W<sup>1</sup></td> </tr> <tr height="1" bgcolor="#829EBA"><td colspan="4"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td></tr> </table> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1" alt="1"> <p>These particular constants were chosen after having been identified as being the best choice, taking into account the previous definition of the SI, which was based on seven base units, and progress in science.</p> <p>The definitions below specify the exact numerical value of each constant when its value is expressed in the corresponding SI unit. By fixing the exact numerical value the unit becomes defined, since the product of the <i><b>numerical value</b></i> and the <i><b>unit</b></i> has to equal the <i><b>value</b></i> of the constant, which is postulated to be invariant. The seven constants are chosen in such a way that any unit of the SI can be written either through a defining constant itself or through products or quotients of defining constants.</p> <center> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="3" alt=""> <table width="100%" bgcolor="#829EBA" cellspacing="3" cellpadding="10"><tr><td bgcolor="#FFFFFF"> <p>The International System of Units, the SI, is the system of units in which</p> <ul> <li>the unperturbed ground state hyperfine transition frequency of the caesium 133 atom <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/nu.gif" alt="nu"><sub>Cs</sub> is 9 192 631 770 Hz,</nobr></li> <li>the speed of light in vacuum <i>c</i> is <nobr>299 792 458 m/s,</nobr></li> <li>the Planck constant <i>h</i> is <nobr>6.626 070 15 x 10<sup>34</sup> J s,</nobr></li> <li>the elementary charge <i>e</i> is <nobr>1.602 176 634 x 10<sup>19</sup> C,</nobr></li> <li>the Boltzmann constant <i>k</i> is <nobr>1.380 649 x 10<sup>23</sup> J/K,</nobr></li> <li>the Avogadro constant <i>N</i><sub>A</sub> is <nobr>6.022 140 76 x 10<sup>23</sup> mol<sup>1</sup>,</nobr></li> <li>the luminous efficacy of monochromatic radiation of frequency <nobr>540 x 10<sup>12</sup> Hz,</nobr> <nobr><i>K</i><sub>cd</sub>,</nobr> is <nobr>683 lm/W.</nobr></li> </ul> </td></tr></table> </center> <p>where the hertz, joule, coulomb, lumen, and watt, with unit symbols Hz, J, C, lm, and W, respectively, are related to the units second, metre, kilogram, ampere, kelvin, mole, and candela, with unit symbols s, m, kg, A, K, mol, and cd, respectively, according to Hz = s<sup>1</sup>, J = kg m<sup>2</sup> s<sup>2</sup>, C = A s, lm = cd m<sup>2</sup> m<sup>2</sup> = cd sr, and W = kg m<sup>2</sup> s<sup>3</sup>.</p> <p>The seven constants are chosen in such a way that any unit of the SI can be written either through a defining constant itself or through products or quotients of defining constants.</p> <p>The numerical values of the seven defining constants have no uncertainty.</p> </ul> </div> <div id="si-base-units" class="txt12pt"> <ul> <script> $(function() { $("#accordion").accordion({ heightStyle: "content", }); }); </script> <table align="right" cellpadding="15" border="0"><tr><td> <a href="/web/20200524105425/https://www.bipm.org/en/si-download-area/"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/logos/revised-SI-logo.png" width="250" height="250" border="0"></a></td></tr></table> <p><b>The SI base units:</b></p> <center> <table align="right" border="0"> <tr height="1" bgcolor="#829EBA"> <td colspan="5"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td></tr> <tr> <td class="txt11ptg" colspan="2"><center>Base quantity</center></td> <td width="10"></td> <td class="txt11ptg" colspan="2"><center>Base unit</center></td> </tr> <tr height="1"> <td colspan="2" width="300" bgcolor="#829EBA"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td> <td width="10"></td> <td colspan="2" width="300" bgcolor="#829EBA"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td> </tr> <tr> <td class="txt11ptg" width="150">Name</td> <td class="txt11ptg" width="150">Typical symbol</td> <td></td> <td class="txt11ptg" width="150">Name</td> <td class="txt11ptg" width="150">Symbol</td> </tr> <tr height="1" bgcolor="#829EBA"> <td colspan="5"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td></tr> <tr> <td class="txt11ptl">time</td> <td class="txt11ptl"><i>t</i></td> <td></td> <td class="txt11ptl">second</td> <td class="txt11ptl">s</td> </tr> <tr> <td class="txt11ptl">length</td> <td class="txt11ptl"><i>l</i>, <i>x</i>, <i>r</i>, etc.</td> <td></td> <td class="txt11ptl">metre</td> <td class="txt11ptl">m</td> </tr> <tr> <td class="txt11ptl">mass</td> <td class="txt11ptl"><i>m</i></td> <td></td> <td class="txt11ptl">kilogram</td> <td class="txt11ptl">kg</td> </tr> <tr> <td class="txt11ptl">electric current</td> <td class="txt11ptl"><i>I</i>, <i>i</i></td> <td></td> <td class="txt11ptl">ampere</td> <td class="txt11ptl">A</td> </tr> <tr> <td class="txt11ptl">thermodynamic temperature</td> <td class="txt11ptl"><i>T</i></td> <td></td> <td class="txt11ptl">kelvin</td> <td class="txt11ptl">K</td> </tr> <tr> <td class="txt11ptl">amount of substance</td> <td class="txt11ptl"><i>n</i></td> <td></td> <td class="txt11ptl">mole</td> <td class="txt11ptl">mol</td> </tr> <tr> <td class="txt11ptl">luminous intensity</td> <td class="txt11ptl"><i>I</i><sub>v</sub></td> <td></td> <td class="txt11ptl">candela</td> <td class="txt11ptl">cd</td> </tr> <tr height="1" bgcolor="#829EBA"> <td colspan="5"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="1"></td></tr> </table> </center> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="100%" height="3" alt=""> </ul> <div id="accordion"> <h3>Definitions</h3> <div> <p>Starting from the definition of the SI in terms of fixed numerical values of the defining constants, definitions of each of the seven base units are deduced by using, as appropriate, one or more of these defining constants to give the following set of definitions: </div> <h3>The second</h3> <div> <ul> <p><b>The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/bold/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/ital-bold/nu.gif" alt="nu"><sub>Cs</sub>, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be <nobr>9 192 631 770</nobr> when expressed in the unit Hz, which is equal to s<sup>1</sup>.</b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-s_delta-nu.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub> = 9 192 631 770 Hz. Inverting this relation gives an expression for the unit second in terms of the defining constant <nobr><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub>:</nobr></p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/seconde1.jpg" width="164.4" height="70.8" alt=""></center> or <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/seconde2.jpg" width="164.4" height="70.8" alt=""></center> <p>The effect of this definition is that the second is equal to the duration of <nobr>9 192 631 770</nobr> periods of the radiation corresponding to the transition between the two hyperfine levels of the unperturbed ground state of the <sup>133</sup>Cs atom.</p> </td> </tr> </table> </ul> </div> <h3>The metre</h3> <div> <ul> <p><b>The metre, symbol m, is the SI unit of length. It is defined by taking the fixed numerical value of the speed of light in vacuum <i>c</i> to be 299 792 458 when expressed in the unit m s<sup>1</sup>, where the second is defined in terms of the caesium frequency <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/bold/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/ital-bold/nu.gif" alt="nu"><sub>Cs</sub>.</b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-m_c.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <i>c</i> = <nobr>299 792 458 m s<sup>1</sup>.</nobr> Inverting this relation gives an exact expression for the metre in terms of the defining constants <i>c</i> and <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub>:</p> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/metre1.jpg" width="541.2" height="76.4" alt=""> <p>The effect of this definition is that one metre is the length of the path travelled by light in vacuum during a time interval with duration of <nobr>1/299 792 458</nobr> of a second.</p> </td> </tr> </table> </ul> </div> <h3>The kilogram</h3> <div> <ul> <p><b>The kilogram, symbol kg, is the SI unit of mass. It is defined by taking the fixed numerical value of the Planck constant <i>h</i> to be <nobr>6.626 070 15 x 10<sup>34</sup></nobr> when expressed in the unit <nobr>J s,</nobr> which is equal to <nobr>kg m<sup>2</sup> s<sup>1</sup>,</nobr> where the metre and the second are defined in terms of <i>c</i> and <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/bold/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/ital-bold/nu.gif" alt="nu"><sub>Cs</sub>.</b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-kg_h.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <i>h</i> = <nobr>6.626 070 15 x 10<sup>34</sup> kg m<sup>2</sup> s<sup>1</sup>.</nobr> Inverting this relation gives an exact expression for the kilogram in terms of the three defining constants <i>h</i>, <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub> and <i>c</i>:</p> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/KGEN1.jpg" width="220.8" height="52.4" alt=""> <p>which is equal to</p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/KGEN2.jpg" width="576.8" height="77.6" alt=""></center> <p>The effect of this definition is to define the unit <nobr>kg m<sup>2</sup> s<sup>1</sup></nobr> (the unit of both the physical quantities action and angular momentum). Together with the definitions of the second and the metre this leads to a definition of the unit of mass expressed in terms of the Planck constant <i>h</i>.</p> </td> </tr> </table> </ul> </div> <h3>The ampere</h3> <div> <ul> <p><b>The ampere, symbol A, is the SI unit of electric current. It is defined by taking the fixed numerical value of the elementary charge <i>e</i> to be <nobr>1.602 176 634 x 10<sup>19</sup></nobr> when expressed in the unit C, which is equal to <nobr>A s,</nobr> where the second is defined in terms of <nobr><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/bold/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/ital-bold/nu.gif" alt="nu"><sub>Cs</sub>.</nobr></b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-A_e.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <i>e</i> = <nobr>1.602 176 634 x 10<sup>19</sup> A s.</nobr> Inverting this relation gives an exact expression for the unit ampere in terms of the defining constants <i>e</i> and <nobr><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub>:</nobr></p> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/AMPEN1.jpg" width="247.2" height="58.4" alt=""> <p>which is equal to</p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/AMPEN2.jpg" width="564.4" height="74.4" alt=""></center> <p>The effect of this definition is that one ampere is the electric current corresponding to the flow of <nobr>1/(1.602 176 634 x 10<sup>19</sup>)</nobr> elementary charges per second.</p> </td> </tr> </table> </ul> </div> <h3>The kelvin</h3> <div> <ul> <p><b>The kelvin, symbol K, is the SI unit of thermodynamic temperature. It is defined by taking the fixed numerical value of the Boltzmann constant <i>k</i> to be <nobr>1.380 649 x 10<sup>23</sup></nobr> when expressed in the unit <nobr>J K<sup>1</sup>,</nobr> which is equal to <nobr>kg m<sup>2</sup> s<sup>2</sup> K<sup>1</sup>,</nobr> where the kilogram, metre and second are defined in terms of <i>h</i>, <i>c</i> and <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/bold/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/ital-bold/nu.gif" alt="nu"><sub>Cs</sub>.</b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-K_k.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <i>k</i> = <nobr>1.380 649 x 10<sup>23</sup> kg m<sup>2</sup> s<sup>2</sup> K<sup>1</sup>.</nobr> Inverting this relation gives an exact expression for the kelvin in terms of the defining constants <i>k</i>, <i>h</i> and <nobr><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub>:</nobr></p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/KELVINEN1.jpg" width="362" height="59.6" alt=""></center> <p>which is equal to</p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/KELVINEN2.jpg" width="519.2" height="72" alt=""></center> <p>The effect of this definition is that one kelvin is equal to the change of thermodynamic temperature that results in a change of thermal energy <i>k</i> <i>T</i> by <nobr>1.380 649 x 10<sup>23</sup> J.</nobr></p> </td> </tr> </table> </ul> </div> <h3>The mole</h3> <div> <ul> <p><b>The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly <nobr>6.022 140 76 x 10<sup>23</sup></nobr> elementary entities. This number is the fixed numerical value of the Avogadro constant, <i>N</i><sub>A</sub>, when expressed in the unit mol<sup>1</sup> and is called the Avogadro number.</b></p> <p><b>The amount of substance, symbol <i>n</i>, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles. </b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-mol_NA.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <i>N</i><sub>A</sub> = <nobr>6.022 140 76 x 10<sup>23</sup> mol<sup>1</sup>.</nobr> Inverting this relation gives an exact expression for the mole in terms of the defining constant <i>N</i><sub>A</sub>:</p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/MOLEEN.jpg" width="312.4" height="70.4" alt=""></center> <p>The effect of this definition is that the mole is the amount of substance of a system that contains <nobr>6.022 140 76 x 10<sup>23</sup></nobr> specified elementary entities.</p> </td> </tr> </table> </ul> </div> <h3>The candela</h3> <div> <ul> <p><b>The candela, symbol cd, is the SI unit of luminous intensity in a given direction. It is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency <nobr>540 x 10<sup>12</sup> Hz,</nobr> <i>K</i><sub>cd</sub>, to be 683 when expressed in the unit <nobr>lm W<sup>1</sup>,</nobr> which is equal to <nobr>cd sr W<sup>1</sup>,</nobr> or <nobr>cd sr kg<sup>1</sup> m<sup>2</sup> s<sup>3</sup>,</nobr> where the kilogram, metre and second are defined in terms of <i>h</i>, <i>c</i> and <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/bold/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/16/ital-bold/nu.gif" alt="nu"><sub>Cs</sub>.</b></p> <table align="left"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/SI-colour-cd_Kcd.jpg" width="250" height="250" alt=""></td> <td width="15"></td> <td valign="center"> <p>This definition implies the exact relation <i>K</i><sub>cd</sub> = <nobr>683 cd sr kg<sup>1</sup> m<sup>2</sup> s<sup>3</sup></nobr> for monochromatic radiation of frequency <img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"> = <nobr>540 x 10<sup>12</sup> Hz.</nobr> Inverting this relation gives an exact expression for the candela in terms of the defining constants <i>K</i><sub>cd</sub>, <i>h</i> and <nobr><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/delta_maj.gif" alt="Delta"><img src="/web/20200524105425im_/https://www.bipm.org/utils/special/14/ital/nu.gif" alt="nu"><sub>Cs</sub>:</nobr></p> <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/candela1.jpg" width="283.05" height="58.09" alt=""> <p>which is equal to</p> <center><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/rev-si/CANDELAEN.jpg" width="466" height="127.2" alt=""></center> <p>The effect of this definition is that one candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency <nobr>540 x 10<sup>12</sup> Hz</nobr> and has a radiant intensity in that direction of <nobr>(1/683) W/sr.</nobr></p> </td> </tr> </table> </ul> </div> </div> <p><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">All other SI units can be derived from these, by multiplying together different powers of the base units.</p> <br> </ul> </div> <div id="cgpm-2018" class="txt12pt"> <ul> <p><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">In the 2018 revision of the SI, the definitions of four of the SI base units  the kilogram, the ampere, the kelvin and the mole  were changed. Their new definitions are based on fixed numerical values of the Planck constant (<i>h</i>), the elementary charge (<i>e</i>), the Boltzmann constant (<i>k</i>), and the Avogadro constant (<i>N</i><sub>A</sub>), respectively.</p> <p> Further, the definitions of all seven base units of the SI are now uniformly expressed using the explicit-constant formulation. Specific mises en pratique have been drawn up to explain the realization of the definitions of each of the base units in a practical way.</p> <p>The new definitions came into force on 20 May 2019.</p> <table width="100%" bgcolor="#829EBA" cellpadding="3"> <tr> <td bgcolor="#FFFFFF"> <table width="100%" cellpadding="20"><tr><td> <ul class="intro"> <li><a href="/web/20200524105425/https://www.bipm.org/en/CGPM/db/26/1/" class="introGras">Resolution 1 of the CGPM (2018): On the revision of the International System of Units (SI)</a></li> </ul> </td></tr></table> </td> </tr> <tr> <td width="100%" bgcolor="#FFFFFF"> <table width="100%" cellpadding="20"> <tr> <td width="70"> <a href="https://web.archive.org/web/20200524105425/https://www.youtube.com/thebipm" target="new"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/YouTube.png" width="70" border="0" alt=""></a></td> <td class="txt12pt">Connect to the BIPM's YouTube channel to watch a recording of the live open session of the 26th General Conference on Weights and Measures which took place on 16 November 2018:</td> </tr> </table> <div align="center"> <a href="https://web.archive.org/web/20200524105425/https://www.youtube.com/thebipm" class="introGras" target="new">https://www.youtube.com/thebipm</a> </div><br> </td> </tr> <tr> <td bgcolor="#FFFFFF"> <table width="100%" cellpadding="20"><tr><td> <ul class="intro"> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/faqs.html" class="introGras">FAQs about the revision of the SI, that came into force on 20 May 2019</a></li><br> <li><a href="/web/20200524105425/https://www.bipm.org/utils/common/pdf/SI-statement.pdf" class="introGras">Information for users about the revision of the SI <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0"></a></li><br> <li><a href="/web/20200524105425/https://www.bipm.org/utils/common/pdf/SI-roadmap.pdf" class="introGras">SI roadmap <img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0"></a> (updated 2018)</li><br> <li><a href="/web/20200524105425/https://www.bipm.org/en/CGPM/db/25/1/" class="introGras">Resolution 1 of the CGPM (2014): On the future revision of the International System of Units, the SI</a></li><br> <li><a href="/web/20200524105425/https://www.bipm.org/en/CGPM/db/24/1/" class="introGras">Resolution 1 of the CGPM (2011): On the possible future revision of the International System of Units, the SI</a></li> </ul> </td></tr></table> </td> </tr> <tr> <td bgcolor="#FFFFFF"> <table width="100%" cellpadding="20"><tr><td> <ul class="intro"> <li><a href="/web/20200524105425/https://www.bipm.org/en/si-download-area/" class="introGras">Promotional documents and information about the revision of the SI</a></li> </ul> </td></tr></table> </td> </tr> </table> </ul> </div> <div id="si-en-pratique"> <ul> <p><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt=""> <span class="SousTitre">Appendix 2 of the SI Brochure</span> <p>Thee <i>mises en pratique</i> are prepared by the relevant Consultative Committees, and, after approval by the CIPM, are then published in electronic form here on the BIPM website, where they may be revised more frequently than if they were printed in the SI Brochure.</p></p> <ul> <table width="95%"> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="/web/20200524105425/https://www.bipm.org/utils/en/pdf/SIApp2_s_en.pdf"> Practical realization of the definition of the unit of time</a></td> <td class="txt11ptr">(last updated 1 June 2013)</td> </tr> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="/web/20200524105425/https://www.bipm.org/utils/en/pdf/SIApp2_mol_en.pdf"> Realizing the mole</a></td> <td class="txt11ptr">(last updated 10 October 2012)</td> </tr> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="electrical-units.html"> Practical realization of units for electrical quantities</a></td> <td class="txt11ptr">(last updated 20 February 2007)</td> </tr> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="kilogram.html"> Practical realization of the definition of the kilogram</a></td> <td class="txt11ptr">(last updated 26 September 2005)</td> </tr> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="standard-frequencies.html"> Recommended values of standard frequencies</a></td> <td class="txt11ptr">(last updated 30 November 2018)</td> </tr> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="https://web.archive.org/web/20200524105425/https://doi.org/10.1088/0026-1394/53/3/G1"><i>Mise en pratique</i> for the definition of the candela</a></td> <td class="txt11ptr"> (last updated July 2015)</td> </tr> <tr> <td><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/bullet1.gif" width="16" height="9"> <a class="introGras" href="/web/20200524105425/https://www.bipm.org/en/committees/cc/cct/publications-cc.html#kelvin-and-temperature-scales"><i>Mise en pratique</i> of the definition of the kelvin</a></td> <td class="txt11ptr"> (last updated October 2011)</td> </tr> </table> </ul> </ul> </div> <div id="si-prefixes" class="txt12pt"> <p><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt=""> Decimal multiples and submultiples of SI units can be written using the SI prefixes listed in the table below:</p> <br> <center> <table border="0" cellpadding="5" cellspacing="0" width="80%" class="center" align="center"> <tr height="5" bgcolor="#F2AE30"> </tr> <tr height="30" bgcolor="#F2AE30"> <td align="center" class="txt14ptl">Factor</td> <td align="center" class="txt14ptl">Name</td> <td align="center" class="txt14ptl">Symbol</td> <td align="center" class="txt14ptl">Multiplying Factor</td> </tr> <tr height="1"> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>24</sup></center></td> <td class="txt12pt"><center>yotta</center></td> <td class="txt12pt"><center>Y</center></td> <td class="txt12pt"><center>1 000 000 000 000 000 000 000 000</center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>21</sup></center></td> <td class="txt12pt"><center>zetta</center></td> <td class="txt12pt"><center>Z</center></td> <td class="txt12pt"><center>1 000 000 000 000 000 000 000 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>18</sup></center></td> <td class="txt12pt"><center>exa</center></td> <td class="txt12pt"><center>E</center></td> <td class="txt12pt"><center>1 000 000 000 000 000 000 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>15</sup></center></td> <td class="txt12pt"><center>peta</center></td> <td class="txt12pt"><center>P</center></td> <td class="txt12pt"><center>1 000 000 000 000 000 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>12</sup></center></td> <td class="txt12pt"><center>tera</center></td> <td class="txt12pt"><center>T</center></td> <td class="txt12pt"><center>1 000 000 000 000 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>9</sup></center></td> <td class="txt12pt"><center>giga</center></td> <td class="txt12pt"><center>G</center></td> <td class="txt12pt"><center>1 000 000 000 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>6</sup></center></td> <td class="txt12pt"><center>mega</center></td> <td class="txt12pt"><center>M</center></td> <td class="txt12pt"><center>1 000 000 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>3</sup></center></td> <td class="txt12pt"><center>kilo</center></td> <td class="txt12pt"><center>k</center></td> <td class="txt12pt"><center>1 000 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>2</sup></center></td> <td class="txt12pt"><center>hecto</center></td> <td class="txt12pt"><center>h</center></td> <td class="txt12pt"><center>100 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>1</sup></center></td> <td class="txt12pt"><center>deca</center></td> <td class="txt12pt"><center>da</center></td> <td class="txt12pt"><center>10 </center></td> </tr> <tr height="30"> <th class="txt12pt"><center>10<sup>1</sup></th> <th class="txt12pt"><center>deci</th> <th class="txt12pt"><center>d</th> <td class="txt12pt"><center>0.1 </td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>2</sup></center></td> <td class="txt12pt"><center>centi</center></td> <td class="txt12pt"><center>c</center></td> <td class="txt12pt"><center>0.01 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>3</sup></center></td> <td class="txt12pt"><center>milli</center></td> <td class="txt12pt"><center>m</center></td> <td class="txt12pt"><center>0.001 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>6</sup></center></td> <td class="txt12pt"><center>micro</center></td> <td class="txt12pt"><center>µ</center></td> <td class="txt12pt"><center>0.000 001 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>9</sup></center></td> <td class="txt12pt"><center>nano</center></td> <td class="txt12pt"><center>n</center></td> <td class="txt12pt"><center>0.000 000 001 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>12</sup></center></td> <td class="txt12pt"><center>pico</center></td> <td class="txt12pt"><center>p</center></td> <td class="txt12pt"><center>0.000 000 000 001 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>15</sup></center></td> <td class="txt12pt"><center>femto</center></td> <td class="txt12pt"><center>f</center></td> <td class="txt12pt"><center>0.000 000 000 000 001 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>18</sup></center></td> <td class="txt12pt"><center>atto</center></td> <td class="txt12pt"><center>a</center></td> <td class="txt12pt"><center>0.000 000 000 000 000 001 </center></td> </tr> <tr height="30"> <td class="txt12pt"><center>10<sup>21</sup></center></td> <td class="txt12pt"><center>zepto</center></td> <td class="txt12pt"><center>z</center></td> <td class="txt12pt"><center>0.000 000 000 000 000 000 001 </center></td> </tr> <tr height="30" bgcolor="#DBE3EB"> <td class="txt12pt"><center>10<sup>24</sup></center></td> <td class="txt12pt"><center>yocto</center></td> <td class="txt12pt"><center>y</center></td> <td class="txt12pt"><center>0.000 000 000 000 000 000 000 001 </center></td> </tr> <tr height="1"> </tr> </table> </center> <br> <br> <div class="txt11ptr"><br>[ <a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" class="intros">SI Brochure, Table 5</a> ]</div> <p>For full details please refer to Chapter 3 of the <a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" class="introGras">SI Brochure</a>.</p> </div> </div> </td> <td width="10"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> </tr>  <tr> <td colspan="3" height="5"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="5"></td> </tr> </table></center>   <table width="100%" bgcolor="#D3B657"> <tr> <td width="15%"></td> <td width="1000"> <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td nowrap width="100%"> <style media="all" type="text/css"></style> <div class="menu3"> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/worldwide-metrology/" target="_self">Metrology area:</a></li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/auv/" target="_self">AUV</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/auv/" target="_self">Metrology in the field of Acoustics, Ultrasound and Vibration</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccauv/" target="_self">Committee structure (CCAUV)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/auv/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" target="_self">Units (SI Brochure)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/gpanfilo.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/electricity-magnetism/" target="_self">EM</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/electricity-magnetism/" target="_self">Metrology in the field of Electricity and Magnetism</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccem/" target="_self">Committee structure (CCEM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/electricity-magnetism/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/electricity-magnetism/units.html" target="_self">Units for electrical quantities</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/electricity/" target="_self">BIPM laboratory work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/comparisons/#PM" target="_self">Ongoing BIPM comparisons</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/calibrations/#electricity" target="_self">BIPM calibrations of electrical standards</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/electricity-magnetism/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/mstock.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/length/" target="_self">L</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/length/" target="_self">Length Metrology</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccl/" target="_self">Committee structure (CCL)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/length/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/length/units.html" target="_self">Unit of length (metre)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies.html" target="_self">Recommended values of standard frequencies</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/gpanfilo.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/mass/" target="_self">M</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/mass/" target="_self">Mass Metrology</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccm/" target="_self">Committee structure (CCM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/mass/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/mass/units.html" target="_self">Unit of mass (kilogram)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/mass/" target="_self">BIPM laboratory work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/mass/calibrations_mass/" target="_self">Calibration services</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/mass/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/mass/contact.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/photometry-radiometry/" target="_self">PR</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/photometry-radiometry/" target="_self">Metrology in the field of Photometry and Radiometry</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccpr/" target="_self">Committee structure (CCPR)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/utils/en/pdf/CCPR-strategy-document.pdf" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/photometry-radiometry/units.html" target="_self">Photometric units</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/photometry-radiometry/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/jviallon.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/chemistry-biology/" target="_self">QM</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/chemistry-biology/" target="_self">Metrology in the field of Chemistry and Biology</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccqm/" target="_self">Committee structure (CCQM)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/chemistry-biology/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/chemistry-biology/units.html" target="_self">Unit for amount of substance (mole)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/chemistry/" target="_self">BIPM laboratory work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/comparisons/#QM" target="_self">Comparisons piloted by the BIPM</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/calibrations/#chemistry" target="_self">BIPM calibrations: National ozone standards</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/chemistry-biology/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/chemistry-biology/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/rwielgosz.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/ionizing-radiation/" target="_self">RI</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/ionizing-radiation/" target="_self">Metrology in the field of Ionizing Radiation</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccri/" target="_self">Committee structure (CCRI)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/ionizing-radiation/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/ionizing-radiation/units.html" target="_self">SI units</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/ionizing/radionuclides/sir/" target="_self">International Reference System (SIR)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/ionizing/" target="_self">BIPM laboratory work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/comparisons/#RI" target="_self">Ongoing BIPM comparisons</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/calibrations/#ionizing-radiation" target="_self">BIPM calibrations: Ionization chambers</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/ionizing-radiation/publications.html" target="_self">BIPM publications in the scientific literature</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/scientific-output/monographies-ri.html" target="_self"><i>Monographies</i> BIPM</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/ionizing-radiation/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/steven.judge.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/thermometry/" target="_self">T</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/thermometry/" target="_self">Metrology in Thermometry</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/cct/" target="_self">Committee structure (CCT)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/thermometry/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/thermometry/units.html" target="_self">SI base unit (kelvin)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/susanne.picard.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/metrology/time-frequency/" target="_self">TF</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/time-frequency/" target="_self">Time and Frequency Metrology</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/cctf/" target="_self">Committee structure (CCTF)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/time-frequency/#strategy" target="_self">Strategic plan</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/timescales/time-server.html" target="_self">What time is it?</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/timescales/" target="_self">Timescales</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/time-frequency/units.html" target="_self">Unit of time (second)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/mises-en-pratique/standard-frequencies.html" target="_self">Recommended values of standard frequencies</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/tai/" target="_self">BIPM technical work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/jsp/en/TimeCalibrations.jsp" target="_self">BIPM calibrations for time transfer</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/time-frequency/publications.html" target="_self">BIPM technical publications</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/tai/annual-report.html" target="_self">BIPM Annual Report on Time Activities</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm-services/timescales/time-ftp.html" target="_self">FTP server of the BIPM Time Department</a></li> <li><a href="https://web.archive.org/web/20200524105425/http://webtai.bipm.org/database/html/" target="_self">Time Department Database</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/time-frequency/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/patrizia.tavella.html" target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524105425/https://www.bipm.org/en/measurement-units/" target="_self">U</a> <ul> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/" target="_self">Measurement units: the International System (SI)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/#si-base-units" target="_self">SI base units</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/measurement-units/#prefixes" target="_self">SI prefixes</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/committees/cc/ccu/" target="_self">Consultative Committee for Units (CCU)</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/metrology/units/liaisons.html" target="_self">BIPM liaison and coordination work</a></li> <li><a href="https://web.archive.org/web/20200524105425/http://physics.nist.gov/cuu/Constants/index.html" target="new">CODATA recommended values of the Fundamental Physical Constants</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/extra/codata-tgfc/" target="_self">CODATA Task Group on Fundamental Constants</a></li> <li><a href="/web/20200524105425/https://www.bipm.org/en/bipm/people/estefania.de.mirandes.html" target="_self">BIPM contact</a></li> </ul> </li> </ul> </div> </td> </tr> </table> </td> <td width="15%"></td> </tr> </table>   <table width="100%" bgcolor="#193B7F" alt="mid blue"><tr><td> <center> <table width="1000" bgcolor="#193B7F" border="0" cellspacing="0" cellpadding="0"> <tr height="60"> <td width="20"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="20" height="60" alt=""></td> <td width="470"><div align="left"><a href="/web/20200524105425/https://www.bipm.org/en/conference-centre/directions/" class="navigationBlanc">BIPM - Pavillon de Breteuil F-92312 Sèvres Cedex FRANCE</a></div></td> <td width="100" class="navigationBlanc"><center><a href="/web/20200524105425/https://www.bipm.org/en/about-us/disclaimer.html" class="navigationBlanc">Disclaimer</a><br><a href="/web/20200524105425/https://www.bipm.org/en/about-us/privacy-policy.html" class="navigationBlanc">Privacy Policy</a></center></td> <td width="410"><div align="right"><a href="/web/20200524105425/https://www.bipm.org/en/about-us/disclaimer.html" class="navigationBlanc">Copyright © BIPM all rights reserved</a></div></td> <td width="20"><img src="/web/20200524105425im_/https://www.bipm.org/utils/common/img/pix.gif" width="20" height="60" alt=""></td> </tr> </table> </center> </td></tr></table>  </body> </html>