Metre: Difference between revisions

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{{Short description|SI unit of length}}

:''This article is about the unit of length. For other uses of ''metre'' or ''meter'', see ''[[meter (disambiguation)]]''.''

{{About|the unit of length|other uses of "metre" or "meter"|Meter (disambiguation)}}

{{Unit of length

{{Use British English|date=September 2012}}

|name=metre

{{Use dmy dates|date=April 2020}}

|m=1

{{Infobox unit

|accuracy=3 <!--Number of decimal places-->

| name = metre

| image = Metric standards Rijksmuseum.jpg

| caption = Historical replicas of metric standards, including an iron metre

| standard = [[SI]]

| quantity = [[length]]

| symbol = m<ref>

{{cite web

| url=http://physics.nist.gov/cuu/Units/meter.html

| title=Base unit definitions: Meter

| publisher=[[National Institute of Standards and Technology]]

| access-date=2010-09-28

}}</ref>

| dimension = L

| units1 = [[SI units]]

| inunits1 = {{unbulleted list

| {{val|1000|ul=mm}}

| {{val|0.001|ul=km}}

}}

| units2 = [[imperial units|Imperial]]/[[US customary units|US]] units

| inunits2 = {{unbulleted list

| ≈&thinsp;{{val|1.0936|u=[[Yard|yd]]}}

| ≈&thinsp;{{val|3.2808|u=[[Foot (unit)|ft]]}}

| ≈&thinsp;{{val|39.37|u=[[Inch|in]]}}

}}

| units3 = Nautical units

| inunits3 = ≈&thinsp;{{val|0.00053996|u=[[nautical mile|nmi]]}}

}}

The '''metre''', or '''meter''' ([[American English|US]]), is a measure of [[length]]. It is the [[SI base unit|basic unit]] of [[length]] in the [[metric system]] and in the [[International System of Units]] (SI), used around the world for general and scientific purposes. The symbol for metre is '''m'''. Historically, the metre was defined by the [[French Academy of Sciences]] as 1/10,000,000 of the distance from the equator to the north pole through Paris. Now, it is defined by the [[International Bureau of Weights and Measures]] as the distance travelled by [[light]] in absolute [[vacuum]] in 1/299,792,458 of a [[second]]. This is approximately the distance from floor to hip bone on the average barefoot man.

The '''metre''' (or '''meter''' in [[American and British English spelling differences#-re, -er|US spelling]]; symbol: '''m''') is the [[SI base unit|base unit]] of [[length]] in the [[International System of Units]] (SI). Since 2019, the metre has been defined as the length of the path travelled by light in vacuum during a time interval of {{sfrac|{{val|299792458}}}} of a [[second]], where the second is defined by a [[Caesium standard|hyperfine transition frequency of caesium]].<ref name="SIBrochure9thEd">

Decimal multiples and submultiples of the metre, such as ''[[kilometre]]'' (1000 metres) and ''[[centimetre]]'' (1/100 metre), are indicated by adding [[SI prefix]]es to ''metre'' (see [[#SI_prefixed_forms_of_metre|table]] below).

{{citation

|author=International Bureau of Weights and Measures

|author-link=International Bureau of Weights and Measures

|title=The International System of Units (SI)

|date=20 May 2019

|url=https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9.pdf

|archive-url=https://web.archive.org/web/20211018184555/https://www.bipm.org/documents/20126/41483022/SI-Brochure-9.pdf/fcf090b2-04e6-88cc-1149-c3e029ad8232

|url-status=live

|edition=9th

|isbn=978-92-822-2272-0

|archive-date=18 October 2021

}}</ref>

The metre was originally defined in 1791 by the [[National Constituent Assembly (France)|French National Assembly]] as one ten-millionth of the distance from the [[equator]] to the [[North Pole]] along a [[great circle]], so the [[Earth's circumference|Earth's polar circumference]] is approximately {{val|40,000|u=km}}.

== History ==

The word ''[[wikt:metre|metre]]'' is from the Greek ''metron'' ({{polytonic|μέτρον}}), "a [[wikt:measure|measure]]" via the French ''mètre''. Its first recorded usage in English meaning this unit of length is from 1797.

In 1799, the metre was redefined in terms of a prototype metre bar. The bar used was changed in 1889, and in 1960 the metre was redefined in terms of a certain number of wavelengths of a certain emission line of [[krypton-86]]. The current definition was adopted in 1983 and modified slightly in 2002 to clarify that the metre is a measure of [[proper length]]. From 1983 until 2019, the metre was formally defined as the length of the path travelled by [[light]] in vacuum in {{sfrac|1|{{val|299792458}}}} of a [[second]]. After the [[2019 revision of the SI]], this definition was rephrased to include the definition of a second in terms of the caesium frequency {{math|Δ''&nu;''_Cs}}. This series of amendments did not alter the size of the metre significantly – today Earth's polar circumference measures {{val|40007.863|u=km}}, a change of about 200 [[parts per million]] from the original value of exactly {{val|40,000|u=km}}, which also includes improvements in the accuracy of measuring the circumference.

In the eighteenth century, there were two favoured approaches to the definition of the standard unit of length. One suggested defining the metre as the length of a [[pendulum]] with a half-[[period (physics)|period]] of one [[second]]. The other suggested defining the metre as one ten-millionth of the length of the Earth's [[meridian (geography)|meridian]] along a quadrant, that is the distance from the equator to the north pole. In 1791, the [[French Academy of Sciences]] selected the meridional definition over the pendular definition because the force of [[gravity]] varies slightly over the surface of the Earth, which affects the period of a pendulum. In order to establish a universally accepted foundation for the definition of the metre, measurements of this meridian more accurate than those available at that time were imperative. The [[Bureau des Longitudes]] commissioned an expedition led by [[Delambre]] and [[Pierre Méchain]], lasting from 1792 to 1799, which measured the length of the [[meridian (geography)|meridian]] between [[Dunkerque]] and [[Barcelona]]. This portion of the meridian, which also passes through [[Paris]], was to serve as the basis for the length of the quarter meridian, connecting the [[North Pole]] with the [[Equator]]. However, in 1793, France adopted the metre based on provisional results from the expedition as its official unit of length. Although it was later determined that the first prototype metre bar was short by a fifth of a millimetre due to miscalculation of the flattening of the Earth, this length became the standard. So, the circumference of the [[Earth]] through the poles is approximately forty million metres.

== Spelling ==

[[Image:Platinum-Iridium meter bar.jpg|right|frame|Historical ''International Prototype Metre'' bar, made of an alloy of platinum and iridium, that was the standard from 1889 to 1960.]]

''Metre'' is the standard spelling of the metric unit for length in nearly all English-speaking nations, the exceptions being the United States<ref>

{{cite web

|url=https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.330-2019.pdf

|title=The International System of Units (SI) – NIST

|publisher=[[National Institute of Standards and Technology]]

|___location=US

|date=26 March 2008

|quote=The spelling of English words is in accordance with the United States Government Printing Office Style Manual, which follows Webster's Third New International Dictionary rather than the Oxford Dictionary. Thus the spellings 'meter', 'liter', 'deka', and 'cesium' are used rather than 'metre', 'litre', 'deca', and 'caesium' as in the original BIPM English text.

}}</ref><ref>The most recent official brochure about the International System of Units (SI), written in French by the ''{{lang|fr|Bureau international des poids et mesures}}'', [[International Bureau of Weights and Measures]] (BIPM) uses the spelling ''metre''; an English translation, included to make the SI standard more widely accessible also uses the spelling ''metre'' ([[#bipm2006|BIPM, 2006]], p. 130''ff''). However, in 2008 the U.S. English translation published by the U.S. [[National Institute of Standards and Technology]] (NIST) chose to use the spelling ''meter'' in accordance with the United States Government Printing Office Style Manual. The Metric Conversion Act of 1975 gives the Secretary of Commerce of the US the responsibility of interpreting or modifying the SI for use in the US. The Secretary of Commerce delegated this authority to the Director of the National Institute of Standards and Technology ([[#turner|Turner]]). In 2008, NIST published the US version ([[#taylor2008a|Taylor and Thompson, 2008a]]) of the English text of the eighth edition of the BIPM publication ''{{lang|fr|Le Système international d'unités}} (SI)'' (BIPM, 2006). In the NIST publication, the spellings "meter", "liter" and "deka" are used rather than "metre", "litre" and "deca" as in the original BIPM English text ([[#taylor2008a|Taylor and Thompson (2008a), p. iii]]). The Director of the NIST officially recognised this publication, together with [[#taylor2008b|Taylor and Thompson (2008b)]], as the "legal interpretation" of the SI for the United States ([[#turner|Turner]]). Thus, the spelling ''metre'' is referred to as the "international spelling"; the spelling ''meter'', as the "American spelling".</ref><ref>

{{cite web

|url=http://www.metricationmatters.com/docs/Spelling_metre_or_meter.pdf

|title=Spelling metre or meter

|first=Pat |last=Naughtin

|website=Metrication Matters

|year=2008

|access-date=2017-03-12

|archive-url=https://web.archive.org/web/20161011100154/http://www.metricationmatters.com/docs/Spelling_metre_or_meter.pdf

|archive-date=11 October 2016|url-status=usurped}}</ref><ref>{{cite web |url= http://grammarist.com/spelling/meter-metre/

|title=Meter vs. metre

|website=Grammarist

|date=21 February 2011

|access-date=2017-03-12

}}</ref> and the Philippines<ref>The Philippines uses [[Philippine English|English]] as an official language and this largely follows American English since the country became a colony of the United States. While the law that converted the country to use the [[metric system]] uses ''metre'' ([[#PH-BatasPambansa8|Batas Pambansa Blg. 8]]) following the SI spelling, in actual practice, ''meter'' is used in government and everyday commerce, as evidenced by laws (''kilometer'', [[#PH-RA7160|Republic Act No. 7160]]), Supreme Court decisions (''meter'', [[#PH-GR185240|G.R. No. 185240]]), and national standards (''centimeter'', [[#PH-PNSBAFS181-2016|PNS/BAFS 181:2016]]).</ref> which use ''meter''.

Measuring devices (such as [[ammeter]], [[speedometer]]) are spelled "-meter" in all variants of English.<ref>{{cite encyclopedia

In the 1870s and in light of modern precision, a series of international conferences were held to devise new metric standards. The [[Metre Convention]] (Convention du Mètre) of 1875 mandated the establishment of a permanent [[International Bureau of Weights and Measures]] (BIPM: Bureau International des Poids et Mesures) to be located in [[Sèvres]], France. This new organisation would preserve the new prototype metre and [[kilogram]] when constructed, distribute national metric prototypes, and would maintain comparisons between them and non-metric measurement standards. This organisation created a new prototype bar in 1889 at the first [[General Conference on Weights and Measures]] (CGPM: Conférence Générale des Poids et Mesures), establishing the ''International Prototype Metre'' as the distance between two lines on a standard bar of an alloy of ninety percent [[platinum]] and ten percent [[iridium]], measured at the melting point of ice.

|url=http://dictionary.cambridge.org/results.asp?searchword=ammeter

|archive-url=https://archive.today/20130703210011/http://dictionary.cambridge.org/results.asp?searchword=ammeter

|url-status=dead

|archive-date=3 July 2013

|title=Cambridge Advanced Learner's Dictionary

|year=2008

|publisher=[[Cambridge University Press]]

|access-date=2012-09-19

}}, s.v. ammeter, meter, parking meter, speedometer.</ref> The suffix "-meter" has the same Greek origin as the unit of length.<ref>

{{cite encyclopedia

|title=American Heritage Dictionary of the English Language

|edition=3rd

|year=1992

|___location=Boston

|publisher=[[Houghton Mifflin]]

}}, s.v. meter.</ref><ref>

{{cite web

|title=-meter – definition of -meter in English

|url=https://en.oxforddictionaries.com/definition/-meter

|archive-url=https://web.archive.org/web/20170426153254/https://en.oxforddictionaries.com/definition/-meter

|url-status=dead

|archive-date=26 April 2017

|publisher=Oxford Dictionaries

}}</ref>

== Etymology ==

In 1893, the standard metre was first measured with an [[interferometer]] by [[Albert Abraham Michelson|Albert A. Michelson]], the inventor of the device and an advocate of using some particular [[wavelength]] of [[light]] as a standard of distance. By 1925, [[interferometry]] was in regular use at the BIPM. However, the International Prototype Metre remained the standard until 1960, when the eleventh [[General Conference on Weights and Measures|CGPM]] defined the metre in the new [[SI]] system as equal to 1,650,763.73 [[wavelength]]s of the [[orange (colour)|orange]]-[[red]] [[emission line]] in the [[electromagnetic spectrum]] of the [[krypton]]-86 [[atom]] in a [[vacuum]]. The original international prototype of the metre is still kept at the BIPM under the conditions specified in 1889.

The etymological roots of ''metre'' can be traced to the Greek verb {{lang|grc|μετρέω}} ({{transliteration|grc|metreo}}) ((I) measure, count or compare)<ref>{{LSJ|metre/w|μετρέω|ref}}.</ref> and noun {{lang|grc|μέτρον}} ({{transliteration|grc|metron}}) (a measure),<ref>{{LSJ|me/tron|μέτρον|shortref}}.</ref> which were used for physical measurement, for poetic metre and by extension for moderation or avoiding extremism (as in "be measured in your response"). This range of uses is also found in Latin ({{lang|la|metior, mensura}}), French ({{lang|fr|mètre, mesure}}), English and other languages. The Greek word is derived from the Proto-Indo-European root ''[[wikt:*meh₁-|*meh₁-]]'' 'to measure'. The motto {{lang|grc|ΜΕΤΡΩ ΧΡΩ}} ({{transliteration|grc|metro chro}}) in the seal of the [[International Bureau of Weights and Measures]] (BIPM), was approved by [[Adolphe Hirsch]] on 11 July 1875 and may be translated as "Keep the measure", thus calls for both measurement and moderation.<ref name=":6">{{Cite web |title=History – The BIPM 150 |url=https://thebipm150.org/history/ |access-date=2025-01-24 |language=}}</ref> The use of the word ''metre'' (for the French unit {{lang|fr|mètre}}) in English began at least as early as 1797.<ref name="Oxford">[[Oxford English Dictionary]], Clarendon Press 2nd ed. 1989, vol. IX p. 697 col. 3.</ref>

== History of definition ==

To further reduce uncertainty, the seventeenth CGPM in 1983 replaced the definition of the metre with its current definition, thus fixing the length of the metre in terms of [[time]] and the [[speed of light]]:

{{excerpt|History of the metre}}

== SI prefixed forms of metre ==

:''The metre is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second.''<ref>[http://www.bipm.org/jsp/en/ViewCGPMResolution.jsp?CGPM=17&RES=1 Resolution 1 of the seventeenth CGPM (1983): Definition of the metre]</ref>

{{Main|Orders of magnitude (length)}}

[[SI prefix]]es can be used to denote decimal multiples and submultiples of the metre, as shown in the table below. Long distances are usually expressed in km, [[astronomical unit]]s (149.6&nbsp;Gm), [[light-year]]s (10&nbsp;Pm), or [[parsec]]s (31&nbsp;Pm), rather than in Mm or larger multiples; "30&nbsp;cm", "30&nbsp;m", and "300&nbsp;m" are more common than "3&nbsp;dm", "3&nbsp;dam", and "3&nbsp;hm", respectively.

The terms ''[[micron]]'' and ''[[millimicron]]'' have been used instead of ''micrometre'' (μm) and ''nanometre'' (nm), respectively, but this practice is discouraged.<ref>[[#taylor2008b|Taylor & Thompson 2003, p. 11.]]</ref>

Note that this definition had the effect of fixing the speed of light in a vacuum at precisely 299,792,458 metres per second. Although the metre is now ''defined'' in terms of time-of-flight, actual laboratory realisations of the metre are still ''delineated'' by counting the required number of wavelengths of light along the distance. An intended byproduct of the 17^th CGPM’s definition was that it enabled scientists to measure their lasers’ wavelengths with one-fifth the uncertainty. To further facilitate reproducibility from lab to lab, the 17^th CGPM also made the iodine-stabilised Helium-Neon laser “a recommended radiation” for realising the metre.<ref>Reference: [http://www.mel.nist.gov/div821/museum/timeline.htm ''Time Line for the Definition of the Meter''] by the NIST.</ref> Today’s best determination of the wavelength of this laser is λ_HeNe&nbsp;=&nbsp;632.991<FONT SIZE="-2">&nbsp;</FONT>398<FONT SIZE="-2">&nbsp;</FONT>22&nbsp;nm with an estimated relative standard uncertainty ''(U)'' of ± &nbsp;2.5&nbsp;×&nbsp;10^-11. This uncertainty is currently the limiting factor in laboratory realisations of the metre as it is several orders of magnitude poorer than that of the second (''U''&nbsp;=&nbsp;1&nbsp;×&nbsp;10^-14). Consequently, a practical realisation of the metre is usually delineated (not defined) today in labs as 1,579,800.298<FONT SIZE="-2">&nbsp;</FONT>728 ±&nbsp;0.000<FONT SIZE="-2">&nbsp;</FONT>039 wavelengths of Helium-Neon laser light in a vacuum.

{{SI multiples

===Timeline of definition===

| unit=metre

* [[1790]][[May 8]] &mdash; The [[National Assembly (French Revolution)|French National Assembly]] decides that the length of the new metre would be equal to the length of a [[pendulum]] with a half-[[period (physics)|period]] of one [[second]].

| symbol=m

| xd=[[decimetre]]

* [[1791]][[March 30]] &mdash; The French National Assembly accepts the proposal by the [[French Academy of Sciences]] that the new definition for the metre be equal to one ten-millionth of the length of the Earth's [[meridian (geography)|meridian]] along a quadrant through Paris, that is the distance from the equator to the north pole.

| xda=[[decametre]]

| xc=[[centimetre]]

* 1795 &mdash; Provisional metre bar constructed of [[brass]].

| xh=[[hectometre]]

| xm=[[millimetre]]

* [[1799]][[December 10]] &mdash; The French National Assembly specifies that the platinum metre bar, constructed on [[23 June]] [[1799]] and deposited in the [[National Archives of France|National Archives]], as the final standard.

| xk=[[kilometre]]

| xmc=[[micrometre]]

* [[1889]][[September 28]] &mdash; The first [[General Conference on Weights and Measures]] (CGPM) defines the length as the distance between two lines on a standard bar of an alloy of [[platinum]] with ten percent [[iridium]], measured at the melting point of ice.

| xn=[[nanometre]]

| xp=[[picometre]]

* [[1927]][[October 6]] &mdash; The seventh CGPM adjusts the definition of the length to be the distance, at 0&nbsp;°[[Celsius|C]], between the axes of the two central lines marked on the prototype bar of platinum-iridium, this bar being subject to one standard [[atmospheric pressure|atmosphere of pressure]] and supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 millimetres from each other.

| xf=[[femtometre]]

}}

* [[1960]][[October 20]] &mdash; The eleventh CGPM defines the length to be equal to 1,650,763.73 [[wavelength]]s in [[vacuum]] of the [[electromagnetic radiation|radiation]] corresponding to the transition between the 2p¹⁰ and 5d⁵ quantum levels of the [[krypton]]-86 [[atom]].

* [[1983]][[October 21]] &mdash; The seventeenth CGPM defines the length as equal to the distance travelled by [[light]] in [[vacuum]] during a time interval of 1/299 792 458 of a [[second]].

==SI prefixed forms of metre==

[[SI prefix]]es are often employed to denote decimal multiples and submultiples of the metre. The most commonly used factors of metre are listed below in '''bold'''.<ref>The term “most commonly used” is based on those with more than 5 million Google hits on the American spelling.</ref>

== Equivalents in other units ==

{| border="1" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f5f5f5; border: 2px #525252 solid; border-collapse: collapse; font-size: 95%;"

{| class=wikitable style="margin:0 auto;"

|-

! colspan="5" style="text-align:left;"|Metric unit<br/>expressed in non-SI units

|colspan="3" style="background:#454545" align="center"|<font color=WHITE>Submultiples</font>||colspan="1" style="background:#454545" align="center"|<font color=WHITE></font>||colspan="3" style="background:#454545" align="center"|<font color=WHITE>Multiples</font>

! colspan="4" style="text-align:left;"|Non-SI unit<br/>expressed in metric units

|-

| 1&nbsp;metre ||≈ ||style="text-align:right;"|1.0936 ||[[yard]]||

|style="background:#d4d4d4" align="center"|'''Factor'''

| 1&nbsp;yard||= ||style="text-align:right;"|0.9144 ||metre

|style="background:#d4d4d4" align="center"|'''Name'''

|style="background:#d4d4d4" align="center"|'''Symbol'''

|style="background:#d4d4d4" align="center"|

|style="background:#d4d4d4" align="center"|'''Factor'''

|style="background:#d4d4d4" align="center"|'''Name'''

|style="background:#d4d4d4" align="center"|'''Symbol'''

|-

| 1&nbsp;metre ||≈ ||style="text-align:right;"|39.370 ||[[inch]]es||

|align="center"|10^&minus;1

| 1&nbsp;inch||= ||style="text-align:right;"|0.0254 ||metre

|decimetre

|align="center"|dm

|

|align="center"|10¹

|decametre

|align="center"|dam

|-

| 1&nbsp;[[centimetre]] ||≈ ||style="text-align:right;"|{{val|0.39370}} ||inch||

|align="center"|10^&minus;2

| 1&nbsp;inch||= ||style="text-align:right;"|2.54 ||centimetres

|'''centimetre'''

|align="center"|cm

|

|align="center"|10²

|hectometre

|align="center"|hm

|-

| 1&nbsp;[[millimetre]] ||≈ ||style="text-align:right;"|{{val|0.039370}} ||inch||

|align="center"|10^&minus;3

| 1&nbsp;inch||= ||style="text-align:right;"|25.4 ||millimetres

|'''millimetre'''

|align="center"|mm

|

|align="center"|10³

|'''kilometre'''

|align="center"|km

|-

| 1&nbsp;metre ||= ||style="text-align:right;"|10{{sup|10}}||[[ångström]]||

|align="center"|10^&minus;6

| 1&nbsp;ångström||= ||style="text-align:right;"|10{{sup|−10}} ||metre

|'''micrometre'''

|align="center"|µm

|

|align="center"|10⁶

|megametre

|align="center"|Mm

|-

| 1&nbsp;[[nanometre]] ||= ||style="text-align:right;"|10||ångström||

|align="center"|10^&minus;9

| 1&nbsp;ångström||= ||style="text-align:right;"|100 ||[[picometre]]s

|'''nanometre'''

|align="center"|nm

|

|align="center"|10⁹

|gigametre

|align="center"|Gm

|-

|align="center"|10^&minus;12

|picometre

|align="center"|pm

|

|align="center"|10¹²

|terametre

|align="center"|Tm

|-

|align="center"|10^&minus;15

|femtometre (fermi)

|align="center"|fm

|

|align="center"|10¹⁵

|petametre

|align="center"|Pm

|-

|align="center"|10^&minus;18

|attometre

|align="center"|am

|

|align="center"|10¹⁸

|exametre

|align="center"|Em

|-

|align="center"|10^&minus;21

|zeptometre

|align="center"|zm

|

|align="center"|10²¹

|zettametre

|align="center"|Zm

|-

|align="center"|10^&minus;24

|yoctometre

|align="center"|ym

|

|align="center"|10²⁴

|yottametre

|align="center"| Ym

|}

Within this table, "inch" and "yard" mean "international inch" and "international yard"<ref>[[#AstinKaro1959|Astin & Karo 1959]].</ref> respectively, though approximate conversions in the left column hold for both international and survey units.

: "≈" means "is approximately equal to";

: "=" means "is exactly equal to".

One metre is exactly equivalent to {{sfrac|5 000|127}}&nbsp;inches and to {{sfrac|1 250|1 143}}&nbsp;yards.

==Equivalents in other units==

<!-- 1 metre ≈ 39.370 078 740 157 5 in / or 39.375 in = 1000.125 mm // what is this for? -->

{| class="wikitable"

|-

A simple [[mnemonic]] to assist with conversion is "three 3s": 1&nbsp;metre is nearly equivalent to 3&nbsp;[[Foot (unit)|feet]] {{frac|3|3|8}}&nbsp;inches. This gives an overestimate of 0.125&nbsp;mm.

! SI value !! Other unit

|-

| 1 metre || 10000/254 ≈ 39.37 [[inch]]es

|-

| 2.54 centimetres || 1 inch

|-

| 1 nanometre || 10 [[ångström]]s

|}

The ancient Egyptian [[cubit]] was about 0.5&nbsp;m (surviving rods are 523–529&nbsp;mm).<ref>Arnold Dieter (1991). [https://books.google.com/books?id=DU04vCP_TFAC ''Building in Egypt: pharaonic stone masonry'']. Oxford: Oxford University Press. {{ISBN|978-0-19-506350-9}}. p.251.</ref> Scottish and English definitions of the [[ell]] (2&nbsp;cubits) were 941&nbsp;mm (0.941&nbsp;m) and 1143&nbsp;mm (1.143&nbsp;m) respectively.<ref>{{Cite web |url=http://www.dsl.ac.uk/getent4.php?plen=7441&startset=10747969&query=ELL&fhit=ell&dregion=form&dtext=snd#fhit |title=Dictionary of the Scots Language |access-date=2011-08-06 |archive-url=https://web.archive.org/web/20120321184808/http://www.dsl.ac.uk/getent4.php?plen=7441&startset=10747969&query=ELL&fhit=ell&dregion=form&dtext=snd#fhit |archive-date=2012-03-21 |url-status=dead }}</ref><ref>{{Cite book |url=https://books.google.com/books?id=-BHnAAAAMAAJ&pg=PA221 |title=The Penny Magazine of the Society for the Diffusion of Useful Knowledge |publisher=Charles Knight |pages=221–22 |date=1840-06-06 |df=dmy-all}}</ref> The ancient Parisian ''toise'' (fathom) was slightly shorter than 2&nbsp;m and was standardised at exactly 2&nbsp;m in the [[mesures usuelles]] system, such that 1&nbsp;m was exactly {{frac|1|2}}&nbsp;toise.<ref name=H&H>{{cite web |url = https://archive.org/details/outlinesofevolut00halluoft/page/66 |title = Outlines of the evolution of weights and measures and the metric system |first1 = William |last1 = Hallock |first2 = Herbert T |last2 = Wade |publisher = The Macmillan Company |year = 1906 |pages = 66–69|___location = London}}</ref> The Russian [[verst]] was 1.0668&nbsp;km.{{sfn|Cardarelli|2004}} The [[Scandinavian mile|Swedish mil]] was 10.688&nbsp;km, but was changed to 10&nbsp;km when Sweden converted to metric units.<ref>{{cite encyclopedia |url=https://snl.no/mil |title=Mil |encyclopedia=Store norske leksikon |first=Knut |last=Hofstad |access-date=2019-10-18 |df=dmy-all}}</ref>

==See also==

*[[Metric system]]

== See also ==

*[[SI]] (International System of Units)

{{Commons category}}

*[[SI prefix]]

{{Wiktionary|metre}}

*[[Conversion of units]] for comparisons with other units

* [[ISO 1]]{{spaced ndash}}standard reference temperature for length measurements

*[[Orders of magnitude (length)]]

* [[Speed ofMetric lightprefix]]

* [[Metrication]]

== References ==

{{Reflist|30em}}

* Bureau International des Poids et Mesures. [http://www1.bipm.org/en/si/history-si/evolution_metre.html The BIPM and the evolution of the definition of the metre]. URL accessed on [[2006]] [[June 3]].

* ———. [http://www.bipm.fr/en/convention/resolutions.html Resolutions of the CGPM]. URL accessed on [[2006]] [[June 3]].

* Penzes, William B. at the U.S. National Institute of Standards and Technology Precision Engineering Division ([[2005]] [[December 29]]). [http://www.mel.nist.gov/div821/museum/timeline.htm Time Line for the Definition of the Meter]. URL accessed on [[2006]] [[June 3]].

* U.S. National Institute of Standards and Technology (October 2000). [http://physics.nist.gov/cuu/Units/index.html The NIST Reference on Constants, Units, and Uncertainty: International System of Units (SI)]:

** [http://physics.nist.gov/cuu/Units/units.html SI base units]. URL accessed on [[2006]] [[June 3]].

** [http://physics.nist.gov/cuu/Units/current.html Definitions of the SI base units]. URL accessed on [[2006]] [[June 3]].

** [http://physics.nist.gov/cuu/Units/meter.html Historical context of the SI: meter]. URL accessed on [[2006]] [[June 3]].

=== NotesCited bibliography ===

{{refbegin}}

<references />

* {{Anchor|Alder2002}}{{cite book |title=The Measure of All Things : The Seven-Year Odyssey and Hidden Error That Transformed the World |first=Ken |last=Alder |year=2002 |publisher=Free Press |___location=New York |isbn=978-0-7432-1675-3 |url-access=registration |url=https://archive.org/details/measureofallthin00alde }}

* {{Anchor|AstinKaro1959}}Astin, A. V. & Karo, H. Arnold, (1959), [http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf ''Refinement of values for the yard and the pound''], Washington DC: National Bureau of Standards, republished on National Geodetic Survey web site and the Federal Register (Doc. 59–5442, Filed, 30 June 1959)

* {{Anchor|BarbrowJudson1976}}{{cite book | title=Weights and Measures Standards of the United States, a brief history | first=Lewis V. | last=Judson | others=Derived from a prior work by Louis A. Fisher (1905) | editor-first=Louis E. | editor-last=Barbrow | publisher=[[US Department of Commerce]], [[National Bureau of Standards]] | ___location=US | date=1976-10-01 | orig-year=1963<!-- 1963-03 --> | id=NBS Special Publication 447; NIST SP 447; 003-003-01654-3 | lccn=76-600055 | doi=10.6028/NBS.SP.447}}

* {{Cite book |last=Bigourdan |first=Guillaume |url=https://archive.org/details/lesystmemtri00bigo|title=Le système métrique des poids et mesures; son établissement et sa propagation graduelle, avec l'histoire des opérations qui ont servi à déterminer le mètre et le kilogramme |trans-title=The metric system of weights and measures; its establishment and gradual propagation, with the history of the operations which served to determine the meter and the kilogram |date=1901 |publisher=Gauthier-Villars |___location=Paris}}

* {{cite EB1911|first1=Alexander Ross |last1=Clarke |author1-link=Alexander Ross Clarke |first2=Friedrich Robert |last2=Helmert |author2-link=Friedrich Robert Helmert |date=1911b |wstitle=Earth, Figure of the|volume=8|pages=801–813}}

* {{Anchor|Guedj2001}}{{cite book |title=La Mesure du Monde |trans-title=The Measure of the World |first=Denis |last=Guedj |translator-first=Art |translator-last=Goldhammer |publisher=University of Chicago Press |___location=Chicago |year=2001}}

* {{Anchor|Cardarelli2003}}{{cite book |title=Encydopaedia of scientific units, weights, and measures: their SI equivalences and origins |last=Cardarelli |first=François |year=2003 |publisher=Springer-Verlag London Limited |isbn=978-1-85233-682-0 |chapter=Chapter 2: The International system of Units |chapter-url=http://www.francoiscardarelli.ca/PDF_Files/ESU_Sample_Chapter_Section_1_2.pdf#page=6 |at=Table 2.1, p. 5 |quote=Data from Giacomo, P., Du platine à la lumière [From platinum to light], ''Bull. Bur. Nat. Metrologie'', '''102''' (1995) 5–14. |access-date=2017-01-26 |url=https://archive.org/details/encyclopaediaofs0000card }}

* {{cite book |last=Cardarelli |first=F. |year=2004 |title=Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins |publisher=Springer |edition=2nd |pages=[https://archive.org/details/encyclopaediaofs0000card/page/120 120]–124 |isbn=1-85233-682-X |url=https://archive.org/details/encyclopaediaofs0000card |url-access=registration}}

* {{anchor|nistmetre}}[http://physics.nist.gov/cuu/Units/meter.html ''Historical context of the SI: Meter'']. Retrieved 26 May 2010.

* {{Anchor|NIST2011}}National Institute of Standards and Technology. (27 June 2011). ''[https://www.nist.gov/pml/div688/grp50/primary-frequency-standards.cfm NIST-F1 Cesium Fountain Atomic Clock]''. Author.

* {{Anchor|NPL2010}}National Physical Laboratory. (25 March 2010). ''[http://www.npl.co.uk/science-technology/time-frequency/optical-frequency-standards-and-metrology/research/iodine-stabilised-lasers Iodine-Stabilised Lasers]''. Author.

* {{Anchor|NRC2010}}{{cite web|url=http://www.nrc-cnrc.gc.ca/eng/projects/inms/si-length.html |publisher=National Research Council Canada |title=Maintaining the SI unit of length |date=5 February 2010 |archive-url=https://web.archive.org/web/20111204014454/http://www.nrc-cnrc.gc.ca/eng/projects/inms/si-length.html |archive-date=4 December 2011 |url-status=dead }}

* {{Anchor|PH-BatasPambansa8}}Republic of the Philippines. (2 December 1978). ''[http://www.chanrobles.com/bataspambansabilang8.htm Batas Pambansa Blg. 8: An Act Defining the Metric System and its Units, Providing for its Implementation and for Other Purposes]''. Author.

* {{Anchor|PH-RA7160}}Republic of the Philippines. (10 October 1991). ''[https://www.officialgazette.gov.ph/downloads/1991/10oct/19911010-RA-7160-CCA.pdf Republic Act No. 7160: The Local Government Code of the Philippines]''. Author.

* {{Anchor|PH-GR185240}} Supreme Court of the Philippines (Second Division). (20 January 2010). ''[https://web.archive.org/web/20180427202441/http://sc.judiciary.gov.ph/jurisprudence/2010/january2010/185240.htm G.R. No. 185240]''. Author.

* {{Anchor|taylor2008a}}Taylor, B.N. and Thompson, A. (Eds.). (2008a). [https://web.archive.org/web/20171120061639/https://www.nist.gov/sites/default/files/documents/2016/12/07/sp330.pdf ''The International System of Units (SI)'']. United States version of the English text of the eighth edition (2006) of the International Bureau of Weights and Measures publication ''Le Système International d' Unités (SI)'' (Special Publication 330). Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 18 August 2008.

* {{Anchor|taylor2008b}}Taylor, B.N. and Thompson, A. (2008b). [http://physics.nist.gov/cuu/pdf/sp811.pdf ''Guide for the Use of the International System of Units''] (Special Publication 811). Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 23 August 2008.

* {{Anchor|turner}}Turner, J. (deputy director of the National Institute of Standards and Technology). (16 May 2008). [https://www.nist.gov/pml/wmd/metric/upload/FRN_Vol_73_No_96_16May2008_SI_Interpretation.pdf "Interpretation of the International System of Units (the Metric System of Measurement) for the United States"]. ''Federal Register'' Vol. 73, No. 96, p.{{nbsp}}28432–28433.

* {{Anchor|Zagar1999}}Zagar, B.G. (1999). [https://books.google.com/books?id=VXQdq0B3tnUC&pg=PT164#PPT160,M1 Laser interferometer displacement sensors] in J.G. Webster (ed.). ''The Measurement, Instrumentation, and Sensors Handbook''. CRC Press. {{ISBN|0-8493-8347-1}}.

{{refend}}

{{SI units}}

== External links ==

{{SI units of length}}

* [http://www.mel.nist.gov/div821/museum/length.htm Length—Evolution from Measurement Standard to a Fundamental Constant] at U.S. NIST <!-- Information there not yet included in article -->

{{Authority control}}

* [http://histoire.du.metre.free.fr/en/ The History of the Meter] By Tibo Qorl (Translated by Sibille Rouzaud)

[[Category:Metre| ]]

[[Category:SI base units]]

[[Category:Units of length]]

[[Category:1790s introductions]]

[[af:Meter]]

[[als:Meter]]

[[ar:متر]]

[[ast:Metru]]

[[bn:মিটার]]

[[zh-min-nan:Kong-chhioh]]

[[bs:Metar]]

[[br:Metr]]

[[bg:Метър]]

[[ca:Metre]]

[[cs:Metr]]

[[da:Meter]]

[[de:Meter]]

[[et:Meeter]]

[[el:Μέτρο (μονάδα μήκους)]]

[[es:Metro]]

[[eo:Metro]]

[[eu:Metro]]

[[fa:متر]]

[[fr:Mètre]]

[[gl:Metro]]

[[ko:미터]]

[[hr:Metar]]

[[id:Meter]]

[[ia:Metro]]

[[is:Metri]]

[[it:Metro]]

[[he:מטר]]

[[ka:მეტრი]]

[[sw:Mita]]

[[ku:Mitir]]

[[la:Metrum]]

[[lv:Metrs]]

[[lb:Meter]]

[[hu:Méter]]

[[mt:Metru]]

[[mr:मीटर]]

[[ms:Meter]]

[[nl:Meter]]

[[ja:メートル]]

[[no:Meter]]

[[nn:Meter]]

[[nrm:Mète]]

[[nds:Meter]]

[[pl:Metr]]

[[pt:Metro]]

[[ro:Metru]]

[[ru:Метр]]

[[sco:Metre]]

[[sq:Metri]]

[[simple:Metre]]

[[sk:Meter]]

[[sl:Meter]]

[[sr:Метар]]

[[sh:Metar]]

[[su:Méter]]

[[fi:Metri]]

[[sv:Meter]]

[[tl:Metro]]

[[ta:மீட்டர்]]

[[th:เมตร]]

[[vi:Mét]]

[[tr:Metre]]

[[uk:Метр]]

[[vls:Meter]]

[[zh-yue:米]]

[[zh:米 (单位)]]