metre

{{Short description|SI unit of length}}

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

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

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

{{Infobox unit

| name = metre

| image = Metric standards Rijksmuseum.jpg

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

| standard = SI

| quantity = length

| symbol = m

{{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

}}

| dimension = L

| units1 = SI units

| inunits1 = {{unbulleted list

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

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

}}

| units2 = Imperial/US units

| inunits2 = {{unbulleted list

| ≈ {{val|1.0936|u=yd}}

| ≈ {{val|3.2808|u=ft}}

| ≈ {{val|39.37|u=in}}

}}

| units3 = Nautical units

| inunits3 = ≈ {{val|0.00053996|u=nmi}}

}}

The metre (or meter in US spelling; symbol: m) is the 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 hyperfine transition frequency of caesium.

{{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

}}

The metre was originally defined in 1791 by the 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 polar circumference is approximately {{val|40,000|u=km}}.

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|ΔνCs}}. 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.

Spelling

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

{{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.

}}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 (BIPM, 2006, p. 130ff). 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). In 2008, NIST published the US version (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 (Taylor and Thompson (2008a), p. iii). The Director of the NIST officially recognised this publication, together with Taylor and Thompson (2008b), as the "legal interpretation" of the SI for the United States (Turner). Thus, the spelling metre is referred to as the "international spelling"; the spelling meter, as the "American spelling".

{{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}}{{cite web |url= http://grammarist.com/spelling/meter-metre/

|title=Meter vs. metre

|website=Grammarist

|date=21 February 2011

|access-date=2017-03-12

}} and the PhilippinesThe Philippines uses 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 (Batas Pambansa Blg. 8) following the SI spelling, in actual practice, meter is used in government and everyday commerce, as evidenced by laws (kilometer, Republic Act No. 7160), Supreme Court decisions (meter, G.R. No. 185240), and national standards (centimeter, PNS/BAFS 181:2016). which use meter.

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

|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. The suffix "-meter" has the same Greek origin as the unit of length.

{{cite encyclopedia

|title=American Heritage Dictionary of the English Language

|edition=3rd

|year=1992

|location=Boston

|publisher=Houghton Mifflin

}}, s.v. meter.

{{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

}}

Etymology

The etymological roots of metre can be traced to the Greek verb {{lang|grc|μετρέω}} ({{transliteration|grc|metreo}}) ((I) measure, count or compare){{LSJ|metre/w|μετρέω|ref}}. and noun {{lang|grc|μέτρον}} ({{transliteration|grc|metron}}) (a measure),{{LSJ|me/tron|μέτρον|shortref}}. 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 *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.{{Cite web |title=History – The BIPM 150 |url=https://thebipm150.org/history/ |access-date=2025-01-24 |language=}} The use of the word metre (for the French unit {{lang|fr|mètre}}) in English began at least as early as 1797.Oxford English Dictionary, Clarendon Press 2nd ed. 1989, vol. IX p. 697 col. 3.

History of definition

{{excerpt|History of the metre}}

SI prefixed forms of metre

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

SI prefixes 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 units (149.6 Gm), light-years (10 Pm), or parsecs (31 Pm), rather than in Mm or larger multiples; "30 cm", "30 m", and "300 m" are more common than "3 dm", "3 dam", and "3 hm", respectively.

The terms micron and millimicron have been used instead of micrometre (μm) and nanometre (nm), respectively, but this practice is discouraged.Taylor & Thompson 2003, p. 11.

{{SI multiples

| unit=metre

| symbol=m

| xd=decimetre

| xda=decametre

| xc=centimetre

| xh=hectometre

| xm=millimetre

| xk=kilometre

| xmc=micrometre

| xn=nanometre

| xp=picometre

| xf=femtometre

}}

Equivalents in other units

class=wikitable style="margin:0 auto;"
colspan="5" style="text-align:left;"|Metric unit
expressed in non-SI units

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

1 metrestyle="text-align:right;"|1.0936yard| 1 yard=style="text-align:right;"|0.9144metre
1 metrestyle="text-align:right;"|39.370inches| 1 inch=style="text-align:right;"|0.0254metre
centimetrestyle="text-align:right;"|{{val|0.39370}}inch| 1 inch=style="text-align:right;"|2.54centimetres
millimetrestyle="text-align:right;"|{{val|0.039370}}inch| 1 inch=style="text-align:right;"|25.4millimetres
1 metre=style="text-align:right;"|10{{sup|10}}ångström| 1 ångström=style="text-align:right;"|10{{sup|−10}}metre
nanometre=style="text-align:right;"|10ångström| 1 ångström=style="text-align:right;"|100picometres

Within this table, "inch" and "yard" mean "international inch" and "international yard"Astin & Karo 1959. 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}} inches and to {{sfrac|1 250|1 143}} yards.

A simple mnemonic to assist with conversion is "three 3s": 1 metre is nearly equivalent to 3 feet {{frac|3|3|8}} inches. This gives an overestimate of 0.125 mm.

The ancient Egyptian cubit was about 0.5 m (surviving rods are 523–529 mm).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. Scottish and English definitions of the ell (2 cubits) were 941 mm (0.941 m) and 1143 mm (1.143 m) respectively.{{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 }}{{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}} The ancient Parisian toise (fathom) was slightly shorter than 2 m and was standardised at exactly 2 m in the mesures usuelles system, such that 1 m was exactly {{frac|1|2}} toise.{{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}} The Russian verst was 1.0668 km.{{sfn|Cardarelli|2004}} The Swedish mil was 10.688 km, but was changed to 10 km when Sweden converted to metric units.{{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}}

See also

{{Commons category}}

{{Wiktionary|metre}}

Notes

{{Reflist|30em}}

References

{{refbegin}}

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  • {{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)
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{{refend}}

{{SI units}}

{{SI units of length}}

{{Authority control}}

Category:SI base units