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class="mw-body-content"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><div style="width:200px; clear:both; float:right; padding:0px; margin:1em 0em 1em 1em; font-size: 88%"> <table class="wikitable" align="right" style="font-size: 88% margin:0px; text-align:center"> <tbody><tr> <th colspan="3"><big>Length</big> </th></tr> <tr> <td colspan="2"><b>Dimension</b> </td> <td>L </td></tr> <tr> <td colspan="2"><b>Usual Symbol</b> </td> <td><i>l</i> </td></tr> <tr> <th colspan="3"><b>Coherent units</b> </th></tr> <tr> <td width="60"><b>System</b> </td> <td width="60"><b>Unit</b> </td> <td width="60"><b>Symbol</b> </td></tr> <tr> <td><a href="/w/index.php?title=Units_of_measurement/SI_units&action=edit&redlink=1" class="new" title="Units of measurement/SI units (does not exist)">SI</a> </td> <td>metre </td> <td>m </td></tr> <tr> <td><a href="/w/index.php?title=Units_of_measurement/CGS_units&action=edit&redlink=1" class="new" title="Units of measurement/CGS units (does not exist)">CGS</a> </td> <td>centimetre </td> <td>cm </td></tr> <tr> <td><a href="/w/index.php?title=Units_of_measurement/Imperial_units&action=edit&redlink=1" class="new" title="Units of measurement/Imperial units (does not exist)">Imperial</a> </td> <td>foot </td> <td>ft </td></tr> </tbody></table></div> <p><br /> </p> <meta property="mw:PageProp/toc" /> <div class="mw-heading mw-heading2"><h2 id="SI_units">SI units</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Units_of_Measurement/Length&veaction=edit&section=1" title="Edit section: SI units" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Units_of_Measurement/Length&action=edit&section=1" title="Edit section's source code: SI units"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>The base unit of length in the SI system is the <b>metre</b>. This has had several definitions over time: </p> <dl><dt>1889</dt> <dd>The <a href="https://en.wikipedia.org/wiki/BIPM" class="extiw" title="w:BIPM">International Bureau of Weights and Measures</a> defines the metre as the distance between two marks on a platinum-iridium alloy bar (the <a href="https://en.wikipedia.org/wiki/International_Prototype_Metre" class="extiw" title="w:International Prototype Metre">International Prototype Metre</a>). This prototype is kept in a vault in Sèvres, near Paris.</dd> <dt>1960</dt> <dd>The 11th <a href="https://en.wikipedia.org/wiki/CPGM" class="extiw" title="w:CPGM">General Conference on Weights and Measures</a><sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> redefines the metre in terms of a specific number of wavelengths of light of a specific frequency in a vacuum. It is defined to be 1 650 763.7<b>3</b> wavelengths of the electromagnetic radiation emitted by an electron transitioning between the levels 2p<sub>10</sub> and 5d<sub>5</sub> of the krypton-86 (<sup>86</sup>Kr) atom in a vacuum. The metre is now defined in terms of reproducible physical effects, rather than a synthetic artifact.</dd> <dt>1983</dt> <dd>The 17th General Conference on Weights and Measures<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup> redefines the metre in terms of the distance traversed by light (having a universally constant speed in a vacuum) in a specific time. It is defined as the distance traveled by a beam of light in a vacuum in 1/299 792 45<b>8</b> <a href="/w/index.php?title=Units_of_measurement/Time&action=edit&redlink=1" class="new" title="Units of measurement/Time (does not exist)">second</a>. This is the current definition. This has the effect that the speed of light is defined to be exactly 299 792 45<b>8</b> m/s.</dd></dl> <table class="wikitable" style="text-align:center; margin: 1em auto 1em auto" width="400"> <caption>Conversion of metric units of length<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup> </caption> <tbody><tr> <th colspan="2">A </th> <td rowspan="10"> </td> <th colspan="7">B </th></tr> <tr> <td><b>Unit</b></td> <td><b>Symbol</b> </td> <td><b>pm</b> </td> <td><b>nm</b> </td> <td><b>μm</b> </td> <td><b>mm</b> </td> <td><b>cm</b> </td> <td style="border-left:1px solid black;"><b>m</b> </td> <td style="border-left:1px solid black;"><b>km</b> </td></tr> <tr> <td>picometre </td> <td>pm </td> <td><sup> </sup>1<sup> </sup> </td> <td>10<sup>-3</sup> </td> <td>10<sup>-6</sup> </td> <td>10<sup>-9</sup> </td> <td>10<sup>-10</sup> </td> <td style="border-left:1px solid black;">10<sup>-12</sup> </td> <td style="border-left:1px solid black;">10<sup>-15</sup> </td></tr> <tr> <td>ångström<sup>†</sup> </td> <td>Å </td> <td>10<sup>2</sup> </td> <td>10<sup>−1</sup> </td> <td>10<sup>−4</sup> </td> <td>10<sup>−7</sup> </td> <td>10<sup>−8</sup> </td> <td style="border-left:1px solid black;">10<sup>−10</sup> </td> <td style="border-left:1px solid black;">10<sup>−13</sup> </td></tr> <tr> <td>nanometre </td> <td>nm </td> <td>10<sup>3</sup> </td> <td><sup> </sup>1<sup> </sup> </td> <td>10<sup>−3</sup> </td> <td>10<sup>−6</sup> </td> <td>10<sup>−7</sup> </td> <td style="border-left:1px solid black;">10<sup>−9</sup> </td> <td style="border-left:1px solid black;">10<sup>−12</sup> </td></tr> <tr> <td>micrometre </td> <td>μm </td> <td>10<sup>6</sup> </td> <td>10<sup>3</sup> </td> <td><sup> </sup>1<sup> </sup> </td> <td>10<sup>−3</sup> </td> <td>10<sup>−4</sup> </td> <td style="border-left:1px solid black;">10<sup>−6</sup> </td> <td style="border-left:1px solid black;">10<sup>−9</sup> </td></tr> <tr> <td>millimetre </td> <td>mm </td> <td>10<sup>9</sup> </td> <td>10<sup>6</sup> </td> <td>10<sup>3</sup> </td> <td><sup> </sup>1<sup> </sup> </td> <td>10<sup>−1</sup> </td> <td style="border-left:1px solid black;">10<sup>−3</sup> </td> <td style="border-left:1px solid black;">10<sup>−6</sup> </td></tr> <tr> <td>centimetre </td> <td>cm </td> <td>10<sup>10</sup> </td> <td>10<sup>7</sup> </td> <td>10<sup>4</sup> </td> <td>10<sup>1</sup> </td> <td><sup> </sup>1<sup> </sup> </td> <td style="border-left:1px solid black;">10<sup>−2</sup> </td> <td style="border-left:1px solid black;">10<sup>−5</sup> </td></tr> <tr> <td style="border-top:1px solid black;">metre </td> <td style="border-top:1px solid black;">m </td> <td style="border-top:1px solid black;">10<sup>12</sup> </td> <td style="border-top:1px solid black;">10<sup>9</sup> </td> <td style="border-top:1px solid black;">10<sup>6</sup> </td> <td style="border-top:1px solid black;">10<sup>3</sup> </td> <td style="border-top:1px solid black;">10<sup>2</sup> </td> <td style="border-top:1px solid black; border-left:1px solid black;"><sup> </sup>1<sup> </sup> </td> <td style="border-top:1px solid black; border-left:1px solid black;">10<sup>3</sup> </td></tr> <tr> <td style="border-top:1px solid black;">kilometre </td> <td style="border-top:1px solid black;">km </td> <td style="border-top:1px solid black;">10<sup>15</sup> </td> <td style="border-top:1px solid black;">10<sup>12</sup> </td> <td style="border-top:1px solid black;">10<sup>9</sup> </td> <td style="border-top:1px solid black;">10<sup>6</sup> </td> <td style="border-top:1px solid black;">10<sup>5</sup> </td> <td style="border-top:1px solid black; border-left:1px solid black;">10<sup>3</sup> </td> <td style="border-top:1px solid black; border-left:1px solid black;"><sup> </sup>1<sup> </sup> </td></tr> <tr> <td colspan="10" style="font-size:88%" align="left"> <dl><dd><ul><li>1 <b>A</b> unit = <i>b</i> <b>B</b> units (b given in the table)</li> <li><sup>†</sup> Ångström is accepted for use with, but not defined by the SI system. Its use is officially discouraged by the <a href="https://en.wikipedia.org/wiki/CIPM" class="extiw" title="w:CIPM">CIPM</a>.</li></ul></dd></dl> </td></tr></tbody></table> <div class="mw-heading mw-heading2"><h2 id="Imperial_units">Imperial units</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Units_of_Measurement/Length&veaction=edit&section=2" title="Edit section: Imperial units" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Units_of_Measurement/Length&action=edit&section=2" title="Edit section's source code: Imperial units"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>One international yard is defined as 0.914 <b>4</b> m </p> <div class="mw-heading mw-heading2"><h2 id="Astronomical_units">Astronomical units</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Units_of_Measurement/Length&veaction=edit&section=3" title="Edit section: Astronomical units" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Units_of_Measurement/Length&action=edit&section=3" title="Edit section's source code: Astronomical units"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <div style="clear: both;"></div> <div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Units_of_Measurement/Length&veaction=edit&section=4" title="Edit section: External links" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Units_of_Measurement/Length&action=edit&section=4" title="Edit section's source code: External links"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <div class="mw-heading mw-heading2"><h2 id="References">References</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Units_of_Measurement/Length&veaction=edit&section=5" title="Edit section: References" class="mw-editsection-visualeditor"><span>edit</span></a><span class="mw-editsection-divider"> | </span><a href="/w/index.php?title=Units_of_Measurement/Length&action=edit&section=5" title="Edit section's source code: References"><span>edit source</span></a><span class="mw-editsection-bracket">]</span></span></div> <style data-mw-deduplicate="TemplateStyles:r4267181">.mw-parser-output .reflist{font-size:90%;margin-bottom:0.5em;list-style-type:decimal}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}</style> <div class="reflist"> <div class="mw-references-wrap"><ol class="references"> <li id="cite_note-1"><span class="mw-cite-backlink"><a href="#cite_ref-1">↑</a></span> <span class="reference-text"> <style data-mw-deduplicate="TemplateStyles:r4271529">.mw-parser-output cite.citation{font-style:inherit;word-wrap:break-word}.mw-parser-output .citation q{quotes:"\"""\"""'""'"}.mw-parser-output .citation:target{background-color:rgba(0,127,255,0.133)}.mw-parser-output .id-lock-free a,.mw-parser-output .citation .cs1-lock-free a{background:url("//upload.wikimedia.org/wikipedia/commons/6/65/Lock-green.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-limited a,.mw-parser-output .id-lock-registration a,.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration a{background:url("//upload.wikimedia.org/wikipedia/commons/d/d6/Lock-gray-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .id-lock-subscription a,.mw-parser-output .citation .cs1-lock-subscription a{background:url("//upload.wikimedia.org/wikipedia/commons/a/aa/Lock-red-alt-2.svg")right 0.1em center/9px no-repeat}.mw-parser-output .cs1-ws-icon a{background:url("//upload.wikimedia.org/wikipedia/commons/4/4c/Wikisource-logo.svg")right 0.1em center/12px no-repeat}.mw-parser-output .cs1-code{color:inherit;background:inherit;border:none;padding:inherit}.mw-parser-output .cs1-hidden-error{display:none;color:#d33}.mw-parser-output .cs1-visible-error{color:#d33}.mw-parser-output .cs1-maint{display:none;color:#3a3;margin-left:0.3em}.mw-parser-output .cs1-format{font-size:95%}.mw-parser-output .cs1-kern-left{padding-left:0.2em}.mw-parser-output .cs1-kern-right{padding-right:0.2em}.mw-parser-output .citation .mw-selflink{font-weight:inherit}</style><cite id="CITEREFConférence_Générale_des_Poids_es_Mesures1960" class="citation book cs1"><a href="https://en.wikipedia.org/wiki/CPGM" class="extiw" title="w:CPGM">Conférence Générale des Poids es Mesures</a> <span class="cs1-format">[at Wikipedia]</span>, ed. (1960). <i>Compte rendu des séances de la 11<sup>e</sup> Conférence générale des Poids es Mesures</i>. Paris: Gauthier-Villars. p. 85.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Compte+rendu+des+s%C3%A9ances+de+la+11%3Csup%3Ee%3C%2Fsup%3E+Conf%C3%A9rence+g%C3%A9n%C3%A9rale+des+Poids+es+Mesures&rft.place=Paris&rft.pages=85&rft.pub=Gauthier-Villars&rft.date=1960&rfr_id=info%3Asid%2Fen.wikibooks.org%3AUnits+of+Measurement%2FLength" class="Z3988"></span></span> </li> <li id="cite_note-2"><span class="mw-cite-backlink"><a href="#cite_ref-2">↑</a></span> <span class="reference-text"> <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r4271529"><cite id="CITEREFConférence_Générale_des_Poids_es_Mesures1983" class="citation book cs1">Conférence Générale des Poids es Mesures, ed. (1983). <i>Compte rendu des séances de la 13<sup>e</sup> Conférence générale des Poids es Mesures</i>.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=book&rft.btitle=Compte+rendu+des+s%C3%A9ances+de+la+13%3Csup%3Ee%3C%2Fsup%3E+Conf%C3%A9rence+g%C3%A9n%C3%A9rale+des+Poids+es+Mesures&rft.date=1983&rfr_id=info%3Asid%2Fen.wikibooks.org%3AUnits+of+Measurement%2FLength" class="Z3988"></span></span> </li> <li id="cite_note-3"><span class="mw-cite-backlink"><a href="#cite_ref-3">↑</a></span> <span class="reference-text">After <link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r4271529"><cite id="CITEREFDiem,_K.,_Lentner,_C._(ed.)1970" class="citation book cs1">Diem, K., Lentner, C. (ed.), ed. (1970). "Physics". <i>Documenta Geigy Scientific Tables</i> (7th ed. ed.). Basle <b>Bold text</b>: J.R. Geigy S.A. p. 200.</cite><span title="ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Abook&rft.genre=bookitem&rft.atitle=Physics&rft.btitle=Documenta+Geigy+Scientific+Tables&rft.place=Basle+%27%27%27Bold+text%27%27%27&rft.pages=200&rft.edition=7th+ed.&rft.pub=J.R.+Geigy+S.A.&rft.date=1970&rfr_id=info%3Asid%2Fen.wikibooks.org%3AUnits+of+Measurement%2FLength" class="Z3988"></span> <span class="cs1-visible-error citation-comment"><code class="cs1-code">{{<a href="/wiki/Template:Cite_book" title="Template:Cite book">cite book</a>}}</code>: </span><span class="cs1-visible-error citation-comment"><code class="cs1-code">|edition=</code> has extra text (<a href="/wiki/Help:CS1_errors#extra_text_edition" title="Help:CS1 errors">help</a>)</span>; <span class="cs1-visible-error citation-comment"><code class="cs1-code">|editor=</code> has generic name (<a href="/wiki/Help:CS1_errors#generic_name" title="Help:CS1 errors">help</a>)</span>; <span class="cs1-visible-error citation-comment">line feed character in <code class="cs1-code">|location=</code> at position 6 (<a href="/wiki/Help:CS1_errors#invisible_char" title="Help:CS1 errors">help</a>)</span><span class="cs1-maint citation-comment">CS1 maint: multiple names: editors list (<a href="/wiki/Category:CS1_maint:_multiple_names:_editors_list" title="Category:CS1 maint: multiple names: editors list">link</a>)</span></span> </li> </ol></div> </div></div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?type=1x1&useformat=desktop" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikibooks.org/w/index.php?title=Units_of_Measurement/Length&oldid=2553106">https://en.wikibooks.org/w/index.php?title=Units_of_Measurement/Length&oldid=2553106</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Special:Categories" title="Special:Categories">Category</a>: <ul><li><a href="/wiki/Category:Book:Units_of_Measurement" title="Category:Book:Units of Measurement">Book:Units of Measurement</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:CS1_errors:_invisible_characters" title="Category:CS1 errors: invisible characters">CS1 errors: invisible characters</a></li><li><a href="/wiki/Category:CS1_errors:_generic_name" title="Category:CS1 errors: generic name">CS1 errors: generic name</a></li><li><a href="/wiki/Category:CS1_errors:_extra_text:_edition" title="Category:CS1 errors: extra text: edition">CS1 errors: extra text: edition</a></li><li><a href="/wiki/Category:CS1_maint:_multiple_names:_editors_list" title="Category:CS1 maint: multiple names: editors list">CS1 maint: multiple names: editors list</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 1 September 2013, at 20:46.</li> <li id="footer-info-copyright">Text is available under the <a rel="nofollow" class="external text" href="//creativecommons.org/licenses/by-sa/4.0/">Creative Commons Attribution-ShareAlike License</a>; additional terms may apply. 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