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href="https://web-static.archive.org/_static/css/iconochive.css?v=3PDvdIFv" />  <meta http-equiv="X-UA-Compatible" content="IE=8"/> <title>BIPM - SI Brochure</title> <meta name="description" content="SI Brochure: The International System of Units (SI)"> <script language="javascript" src="/web/20200524171543js_/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/20200524171543/https://www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-38070491-1', 'auto'); ga('send', 'pageview'); </script> <script src="/web/20200524171543js_/https://www.bipm.org/utils/jquery/jquery-1.10.2.min.js"></script> <script 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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/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="90"></td> <td width="180" valign="center" align="left"><a href="/web/20200524171543/https://www.bipm.org/en/about-us/" title="BIPM home page"><img src="/web/20200524171543im_/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/20200524171543/https://search.bipm.org/bipm/en/C="> <table width="180" align="right" valign="top" 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<li><a href="/web/20200524171543/https://www.bipm.org/en/cipm-mra/cipm-mra-documents/" target="_self">CIPM MRA documents</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/cipm-mra/approval-process.html" target="_self">CMC approval process</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/cipm-mra/logo/" target="_self">Use of the CIPM MRA logo</a></li> <li><a href="/web/20200524171543/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/20200524171543/https://www.bipm.org/en/measurement-units/" target="_self"> SI units</a> <ul> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/" target="_self">The International System of Units (SI)</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200524171543/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/20200524171543/https://www.bipm.org/en/publications/mises-en-pratique/" target="_self">How to realize the definitions in practice</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/base-units.html" target="_self">Unit definitions</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/prefixes.html" target="_self">SI prefixes</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/si-download-area/" target="_self">Revised SI: Download area</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/history-si/" target="_self">Brief history of the SI</a></li> </ul> </li> <li><a href="/web/20200524171543/https://www.bipm.org/en/bipm-services/" target="_self"> Services</a> <ul> <li><a href="/web/20200524171543/https://www.bipm.org/en/bipm-services/comparisons/" target="_self">Comparisons piloted by the BIPM</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/bipm-services/calibrations/" target="_self">Calibration and measurement services</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/bipm/tai/" target="_self">Timescales</a></li> <li><a href="https://web.archive.org/web/20200524171543/https://www.bipm.org/kcdb" target="_self"><img src="/web/20200524171543im_/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/20200524171543/https://www.bipm.org/jctlm/" target="_self"><img src="/web/20200524171543im_/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/20200524171543/http://imrr.bipm.org/" target="_self"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img2/logo_imrr_pt.gif" alt="IMRR" vspace="2"></a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="https://web.archive.org/web/20200524171543/http://iopscience.iop.org/0026-1394/" target="metrologia"><i>Metrologia</i></a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/" target="_self">Meetings</a></li> <li><a href="/web/20200524171543/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/20200524171543/https://www.bipm.org/en/bipm/ionizing/radionuclides/sir/" target="_self">International Reference System (SIR)</a></li> </ul> </li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/" target="_self"> Publications</a> <ul> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/mises-en-pratique/" target="_self"><i>Mises en pratique</i></a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/directors-report/" target="_self">Annual Director's Report</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/committees/cipm/publications-cipm.html#ra" target="_self">Financial Report</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/committees/cipm/publications-cipm.html#no" target="_self">Notification of Contributions</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/" target="_self">Official proceedings</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/worldwide-metrology/cgpm/resolutions.html" target="_self">Resolutions of the General Conference</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/open-literature/" target="_self">Scientific output</a></li> <li><a href="https://web.archive.org/web/20200524171543/http://iopscience.iop.org/0026-1394/" target="metrologia"><i>Metrologia</i></a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/guides/" target="_self">Guides in Metrology</a></li> </ul> </li> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/diary/" target="_self"> Meetings</a> <ul> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/diary/" target="_self">List of meetings</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/" target="_self">BIPM Conference Centre</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/directions/" target="_self">How to get to the BIPM</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/cgpm-2018/" target="_self">General Conference (CGPM)</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/committees/cipm/" target="_self">International Committee (CIPM)</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/committees/cc/" target="_self">Consultative Committees and Working Groups</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/bipm-workshops/" target="_self">BIPM Workshops</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/other-events/" target="_self">Other BIPM events</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/" target="_self">Meeting reports</a></li> <li><a href="/web/20200524171543/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/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="50"></td> <td align="left" width="100%" height="50" background="/web/20200524171543im_/https://www.bipm.org/utils/common/img/cadre_trait.gif"> <table width="100%" border="0" background="/web/20200524171543im_/https://www.bipm.org/en/publications/si-brochure/"> <tr> <td align="left" class="GrosTitre"><div name="exalead-titre">SI Brochure: The International System of Units (SI)</div></td> </tr> </table> </td> <td width="10" height="50"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="50"></td> </tr> </table> </center>  <script> $(function() { $( "#tabs" ).tabs(); $( "#accordion" ).accordion({ heightStyle: "content", collapsible: true }); }); </script>  <center> <table width="1000" border="0" cellspacing="0" cellpadding="0"> <tr> <td width="10"><img src="/web/20200524171543im_/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="#contents">9th edition (2019)</a></li> <li><a href="#appendix1"><a href="/web/20200524171543/https://www.bipm.org/en/publications/si-brochure/appendix1.html">Appendix 1</a></li> <li><a href="#mises-en-pratique"><a href="/web/20200524171543/https://www.bipm.org/en/publications/mises-en-pratique/">Appendix 2</a></li> <li><a href="#appendix3"><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-App3-EN.pdf">Appendix 3</a></li> <li><a href="#appendix4"><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-App4-EN.pdf">Appendix 4</a></li> <li><a href="#previous">Previous editions</a></li> </ul> <div id="contents"> <p><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">We are pleased to present the 9th edition of the SI Brochure (2019), which defines and presents the <i>Système International d'Unités</i>, the SI (known in English as the International System of Units).</p> <ul> <table width="100%" bgcolor="#829EBA" cellpadding="20" cellspacing="3"><tr><td bgcolor="#FFFFFF"> <ul> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf"><b>Complete brochure</b> <img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0"></a> (French and English)</li><br> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-concise-EN.pdf">Concise summary<img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0"></a></li><br> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-EN.pdf">Text in English <img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0"></a></li><br> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-FR.pdf">Text in French<img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" border="0"></a></li><br> </ul> <hr width="90%" align="left" color="#829EBA"> <br> <ul><ul> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/en/publications/si-brochure/appendix1.html">Appendix 1: Decisions of the CGPM and the CIPM</a></li><br> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/en/publications/mises-en-pratique/">Appendix 2: Practical realization of the definition of some important units</a></li><br> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-App3-EN.pdf">Appendix 3: Units for photochemical and photobiological quantities</a></li><br> <li><a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-App4-EN.pdf">Appendix 4: Historical notes on the developpment of the SI and its base units</a></li> </ul></ul> </td></tr></table> </ul> <br> <center> <a rel="license" href="https://web.archive.org/web/20200524171543/http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons Licence" style="border-width:0" src="https://web.archive.org/web/20200524171543im_/https://i.creativecommons.org/l/by/4.0/88x31.png"/></a><br/><span class="txt12pt">NOTE: This work is licensed under a <a rel="license" href="https://web.archive.org/web/20200524171543/http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.</span> </center> <br> </div> <div id="previous"> <p class="SousTitre"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/fleche_jaune.gif" width="29" height="14" alt="">Previous editions of the SI Brochure</p> <center> <table width="90%"> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_8.pdf">8th edition (2006)</a> (French and English) and <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_supplement_2014.pdf">Supplement 2014: updates to the 8th edition</a></td> </tr> <tr><td> </td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_7.pdf">7th edition (1998)</a> (French and English) </td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_6.pdf">6th edition (1991)</a> (French and English) </td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_5.pdf">5th edition (1985)</a> (French and English) </td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_4.pdf">4th edition (1981)</a> (French only) </td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_3.pdf">3rd edition (1977)</a> (French only) </td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_2.pdf">2nd edition (1973)</a> (French only)</td> </tr> <tr> <td width="25" valign="top"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pdf.gif" width="16" height="16" alt="PDF"></td> <td class="txt11ptl"> <a class="introGras" href="/web/20200524171543/https://www.bipm.org/utils/common/pdf/si_brochure_1.pdf">1st edition (1970)</a> (French only)</td> </tr> </table> </center> <br/> </div> </div>  </td> <td width="10" bgcolor="#FFFFFF"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> <td width="160" bgcolor="#829EBA" valign="top"><center><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/si_petit.jpg" width="150" height="216" alt="" border="0"></a></center></td> <td width="10"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="10"></td> </tr> <tr> <td height="5" colspan="5"><img src="/web/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="10" height="5"></td> </tr> </table>   <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/20200524171543/https://www.bipm.org/en/worldwide-metrology/" target="_self">Metrology 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target="_self">BIPM contact</a></li> </ul> </li> <li><a id="" href="/web/20200524171543/https://www.bipm.org/en/measurement-units/" target="_self">U</a> <ul> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/" target="_self">Measurement units: the International System (SI)</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/publications/si-brochure/" target="_self">SI Brochure</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/#si-base-units" target="_self">SI base units</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/measurement-units/#prefixes" target="_self">SI prefixes</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/en/committees/cc/ccu/" target="_self">Consultative Committee for Units (CCU)</a></li> <li><a href="/web/20200524171543/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/20200524171543/http://physics.nist.gov/cuu/Constants/index.html" target="new">CODATA recommended values of the Fundamental Physical Constants</a></li> <li><a href="/web/20200524171543/https://www.bipm.org/extra/codata-tgfc/" target="_self">CODATA Task Group on Fundamental Constants</a></li> <li><a href="/web/20200524171543/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/20200524171543im_/https://www.bipm.org/utils/common/img/pix.gif" width="20" height="60" alt=""></td> <td width="470"><div align="left"><a href="/web/20200524171543/https://www.bipm.org/en/conference-centre/directions/" class="navigationBlanc">BIPM - 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