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This article is about the unit of length. For other uses of "metre" or "meter", see Meter (disambiguation).

metre
Historical public metre standard in Paris
General information
Unit systemSI
Unit oflength
Symbolm[1]
Conversions
1 m[1] in ...... is equal to ...
   SI units   
   Imperial/US units   
  • ≈ 1.0936 yd
  • ≈ 3.2808 ft
  • ≈ 39.37 in
   Nautical units   ≈ 0.00053996 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 ⁠1/299792458⁠ of a second, where the second is defined by a hyperfine transition frequency of caesium.[2]

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 40000 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 ⁠1/299792458⁠ 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 ΔνCs. This series of amendments did not alter the size of the metre significantly – today Earth's polar circumference measures 40007.863 km, a change of about 200 parts per million from the original value of exactly 40000 km, which also includes improvements in the accuracy of measuring the circumference.

Spelling

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Seal of the International Bureau of Weights and Measures (BIPM) – Use measure (Greek: ΜΕΤΡΩ ΧΡΩ)

Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations, the exceptions being the United States[3][4][5][6] and the Philippines[7] which use meter.

Measuring devices (such as ammeter, speedometer) are spelled "-meter" in all variants of English.[8] The suffix "-meter" has the same Greek origin as the unit of length.[9][10]

Etymology

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The etymological roots of metre can be traced to the Greek verb μετρέω (metreo) ((I) measure, count or compare)[11] and noun μέτρον (metron) (a measure),[12] 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 (metior, mensura), French (mètre, mesure), English and other languages. The Greek word is derived from the Proto-Indo-European root *meh₁- 'to measure'. The motto ΜΕΤΡΩ ΧΡΩ (metro chro) in the seal of the International Bureau of Weights and Measures (BIPM), was approuved by Adolphe Hirsch on 11 July 1875 and may be translated as "Keep the measure", thus calls for both measurement and moderation.[13] The use of the word metre (for the French unit mètre) in English began at least as early as 1797.[14]

History of definition

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This section is an excerpt from Arc measurement of Delambre and Méchain.[edit]
At the time of Delambre, it served as a warehouse for all the old weights and measures which were sent by towns throughout France in anticipation of the standardisation of weights and measures by the establishment of the new decimal metric system.[15]

The arc measurement of Delambre and Méchain was a geodetic survey carried out by Jean-Baptiste Delambre and Pierre Méchain in 1792–1798 to measure an arc section of the Paris meridian between Dunkirk and Barcelona. This arc measurement served as the basis for the original definition of the metre.[16]

Until the French Revolution of 1789, France was particularly affected by the proliferation of length measures; the conflicts related to units helped precipitate the revolution. In addition to rejecting standards inherited from feudalism, linking determination of a decimal unit of length with the figure of the Earth was an explicit goal.[17][18] This project culminated in an immense effort to measure a meridian passing through Paris in order to define the metre.

When question of measurement reform was placed in the hands of the French Academy of Sciences, a commission, whose members included Jean-Charles de Borda, Joseph-Louis Lagrange, Pierre-Simon Laplace, Gaspard Monge and the Marquis de Condorcet, decided that the new measure should be equal to one ten-millionth of the distance from the North Pole to the Equator (the quadrant of the Earth's circumference), measured along the meridian passing through Paris at the longitude of Panthéon, which would become the central geodetic station in Paris.[18][15]

In 1791, Jean Baptiste Joseph Delambre and Pierre Méchain were commissioned to lead an expedition to accurately measure the distance between a belfry in Dunkerque and Montjuïc castle in Barcelona in order to calculate the length of the meridian arc through Panthéon.[18][15] The official length of the Mètre des Archives was based on these measurements, but the definitive length of the metre required a value for the non-spherical shape of the Earth, known as the flattening of the Earth.[19] The Weights and Measures Commission would, in 1799, adopt a flattening of ⁠⁠1/334⁠⁠ based on analysis by Pierre-Simon Laplace who combined the French Geodesic Mission to the Equator and the data of the arc measurement of Delambre and Méchain.[20] Combining these two data sets Laplace succeeded to estimate the flattening of the Earth ellipsoid and was happy to find that it also fitted well with his estimate ⁠⁠1/336⁠⁠ based on 15 pendulum measurements.[20][19]

The distance from the North Pole to the Equator was then extrapolated from the measurement of the Paris meridian arc between Dunkirk and Barcelona and the length of the metre was established, in relation to the Toise de l'Académie also called toise of Peru, which had been constructed in 1735 for the French Geodesic Mission to Peru, as well as to Borda's double-toise N°1, one of the four twelve feet (French: pieds) long ruler, part of the baseline measuring instrument devised for this survey.[21][18] When the final result was known, the Mètre des Archives whose length was closest to the meridional definition of the metre was selected and placed in the National Archives on 22 June 1799 (4 messidor An VII in the Republican calendar) as a permanent record of the result.[18]

In 1834, Ferdinand Rudolph Hassler measured at Fire Island the first baseline of the Survey of the Coast,[22] shortly before Louis Puissant declared to the French Academy of Sciences in 1836 that there was an innacuracy in the arc measurement of Delambre and Méchain.[23][24] Ferdinand Rudolph Hassler's use of the metre and the creation of the Office of Standard Weights and Measures as an office within the Coast Survey contributed to the introduction of the Metric Act of 1866 allowing the use of the metre in the United States,[25] and preceded the choice of the metre as international scientific unit of length and the proposal by the 1867 General Conference of the European Arc Measurement (German: Europäische Gradmessung) to establish the International Bureau of Weights and Measures.[26]

Ferdinand Rudolph Hassler was a Swiss-American surveyor who is considered the forefather of both the National Oceanic and Atmospheric Administration (NOAA) and the National Institute of Standards and Technology (NIST) for his achievements as the first Superintendent of the U.S. Survey of the Coast and the first U.S. Superintendent of Weights and Measures.[27][28] The fondation of the United States Coast and Geodetic Survey led to the actual definition of the metre, with Charles Sanders Peirce being the first to experimentally link the metre to the wave length of a spectral line.[29]

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 c to be 299792458 when expressed in the unit m⋅s−1, where the second is defined in terms of the caesium frequency ΔνCs.

Where older traditional length measures are still used, they are now defined in terms of the metre – for example the yard has since 1959 officially been defined as exactly 0.9144 metre.[30]

Early adoptions of the metre internationally

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Main article: Metrication

In France, the metre was adopted as an exclusive measure in 1801 under the Consulate. This continued under the First French Empire until 1812, when Napoleon decreed the introduction of the non-decimal mesures usuelles, which remained in use in France up to 1840 in the reign of Louis Philippe.[31] Meanwhile, the metre was adopted by the Republic of Geneva.[32] After the joining of the canton of Geneva to Switzerland in 1815, Guillaume Henri Dufour published the first official Swiss map, for which the metre was adopted as the unit of length.[33][34]

Adoption dates by country

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SI prefixed forms of metre

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Main article: 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.[37]


SI multiples of metre (m)
Submultiples Multiples
Value SI symbol Name Value SI symbol Name
10−1 m dm decimetre 101 m dam decametre
10−2 m cm centimetre 102 m hm hectometre
10−3 m mm millimetre 103 m km kilometre
10−6 m μm micrometre 106 m Mm megametre
10−9 m nm nanometre 109 m Gm gigametre
10−12 m pm picometre 1012 m Tm terametre
10−15 m fm femtometre 1015 m Pm petametre
10−18 m am attometre 1018 m Em exametre
10−21 m zm zeptometre 1021 m Zm zettametre
10−24 m ym yoctometre 1024 m Ym yottametre
10−27 m rm rontometre 1027 m Rm ronnametre
10−30 m qm quectometre 1030 m Qm quettametre

Equivalents in other units

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Metric unit
expressed in non-SI units 		Non-SI unit
expressed in metric units
1 metre ≈ 1.0936 yard 1 yard = 0.9144 metre
1 metre ≈ 39.370 inches 1 inch = 0.0254 metre
1 centimetre ≈ 0.39370 inch 1 inch = 2.54 centimetres
1 millimetre ≈ 0.039370 inch 1 inch = 25.4 millimetres
1 metre = 1010 ångström 1 ångström = 10−10 metre
1 nanometre = 10 ångström 1 ångström = 100 picometres

Within this table, "inch" and "yard" mean "international inch" and "international yard"[38] 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 ⁠5 000/127⁠ inches and to ⁠1 250/1 143⁠ yards.

A simple mnemonic to assist with conversion is "three 3s": 1 metre is nearly equivalent to 3 feet 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).[39] Scottish and English definitions of the ell (2 cubits) were 941 mm (0.941 m) and 1143 mm (1.143 m) respectively.[40][41] 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 1⁄2 toise.[42] The Russian verst was 1.0668 km.[43] The Swedish mil was 10.688 km, but was changed to 10 km when Sweden converted to metric units.[44]

See also

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Wikimedia Commons has media related to Metre.
Look up metre in Wiktionary, the free dictionary.

Notes

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  1. ^ "Base unit definitions: Meter". National Institute of Standards and Technology. Retrieved 28 September 2010.
  2. ^ International Bureau of Weights and Measures (20 May 2019), The International System of Units (SI) (PDF) (9th ed.), ISBN 978-92-822-2272-0, archived from the original on 18 October 2021
  3. ^ "The International System of Units (SI) – NIST" (PDF). US: National Institute of Standards and Technology. 26 March 2008. 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.
  4. ^ The most recent official brochure about the International System of Units (SI), written in French by the 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 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".
  5. ^ Naughtin, Pat (2008). "Spelling metre or meter" (PDF). Metrication Matters. Archived from the original on 11 October 2016. Retrieved 12 March 2017.
  6. ^ "Meter vs. metre". Grammarist. 21 February 2011. Retrieved 12 March 2017.
  7. ^ The 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).
  8. ^ Cambridge Advanced Learner's Dictionary. Cambridge University Press. 2008. Archived from the original on 3 July 2013. Retrieved 19 September 2012., s.v. ammeter, meter, parking meter, speedometer.
  9. ^ American Heritage Dictionary of the English Language (3rd ed.). Boston: Houghton Mifflin. 1992., s.v. meter.
  10. ^ "-meter – definition of -meter in English". Oxford Dictionaries. Archived from the original on 26 April 2017.
  11. ^ μετρέω. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
  12. ^ μέτρον in Liddell and Scott.
  13. ^ "History – The BIPM 150". Retrieved 24 January 2025.
  14. ^ Oxford English Dictionary, Clarendon Press 2nd ed. 1989, vol. IX p. 697 col. 3.
  15. ^ a b c "How France created the metric system". www.bbc.com. 24 September 2018. Retrieved 9 February 2025.
  16. ^ Alder, K. (2002). The Measure of All Things: The Seven-year Odyssey and Hidden Error that Transformed the World. Free Press. ISBN 978-0-7432-1675-3. Retrieved 2 August 2020.
  17. ^ texte, Académie des sciences (France) Auteur du (1 May 1986). "La Vie des sciences". Gallica (in French). p. 290. Retrieved 19 February 2025.
  18. ^ a b c d e Débarbat, Suzanne; Quinn, Terry (2019). "Les origines du système métrique en France et la Convention du mètre de 1875, qui a ouvert la voie au Système international d'unités et à sa révision de 2018". Comptes Rendus. Physique (in French). 20 (1–2): 6–21. doi:10.1016/j.crhy.2018.12.002. ISSN 1878-1535.
  19. ^ a b Torge, Wolfgang (2016). Rizos, Chris; Willis, Pascal (eds.). "From a Regional Project to an International Organization: The "Baeyer-Helmert-Era" of the International Association of Geodesy 1862–1916". IAG 150 Years. International Association of Geodesy Symposia. 143. Cham: Springer International Publishing: 3–18. doi:10.1007/1345_2015_42. ISBN 978-3-319-30895-1.
  20. ^ a b Nyblom, Jukka (25 April 2023). "How did the meter acquire its definitive length?". GEM - International Journal on Geomathematics. 14 (1): 10. doi:10.1007/s13137-023-00218-9. ISSN 1869-2680.
  21. ^ Delambre, Jean-Baptiste (1749-1822) Auteur du texte; Méchain, Pierre (1744-1804) Auteur du texte (1806–1810). Base du système métrique décimal, ou Mesure de l'arc du méridien compris entre les parallèles de Dunkerque et Barcelone. T. 3 / , exécutée en 1792 et années suivantes, par MM. Méchain et Delambre, rédigée par M. Delambre,... pp. 139, 228.{{cite book}}: CS1 maint: numeric names: authors list (link)
  22. ^ Hassler, Harriet; Burroughs, Charles A. (2007). Ferdinand Rudolph Hassler (1770–1843). NIST Research Library. pp. 51–52.
  23. ^ Lebon, Ernest (1899). Histoire abrégée de l'astronomie / par Ernest Lebon,... pp. 168–171.
  24. ^ Puissant, Louis. Nouvelle détermination de la distance méridienne de Montjouy à Formentera, dévoilant l'inexactitude de celle dont il est fait mention dans la base du système métrique décimal, par M. Puissant,... lu à l'Académie des sciences, le 2 mai 1836.
  25. ^ "Metric Act of 1866 – US Metric Association". usma.org. Retrieved 15 March 2021.
  26. ^ Bericht über die Verhandlungen der vom 30. September bis 7. October 1867 zu BERLIN abgehaltenen allgemeinen Conferenz der Europäischen Gradmessung (PDF) (in German). Berlin: Central-Bureau der Europäischen Gradmessung. 1868. pp. 123–134.
  27. ^ "NOAA 200th Top Tens: History Makers: Ferdinand Rudolph Hassler". US: National Oceanic and Atmospheric Administration. 19 March 2024. Retrieved 17 October 2024.
  28. ^ Cajori, Florian (1921). "Swiss Geodesy and the United States Coast Survey". The Scientific Monthly. 13 (2): 117–129. ISSN 0096-3771.
  29. ^ Crease, Robert P. (1 December 2009). "Charles Sanders Peirce and the first absolute measurement standard". Physics Today. 62 (12): 39–44. doi:10.1063/1.3273015. ISSN 0031-9228.
  30. ^ Nelson, Robert A. (December 1981). "Foundations of the international system of units (SI)" (PDF). The Physics Teacher. 19 (9): 596–613. Bibcode:1981PhTea..19..596N. doi:10.1119/1.2340901.
  31. ^ a b Larousse, Pierre (1866–1877). Grand dictionnaire universel du XIXe siècle : français, historique, géographique, mythologique, bibliographique.... T. 11 MEMO-O / par M. Pierre Larousse. p. 163.
  32. ^ "Metrisches System". hls-dhs-dss.ch (in German). Retrieved 15 December 2021.
  33. ^ "Kartografie". hls-dhs-dss.ch (in German). Retrieved 13 December 2021.
  34. ^ Dufour, G.-H. (1861). "Notice sur la carte de la Suisse dressée par l'État Major Fédéral". Le Globe. Revue genevoise de géographie. 2 (1): 5–22. doi:10.3406/globe.1861.7582.
  35. ^ a b "Metrisches System". hls-dhs-dss.ch (in German). Retrieved 9 December 2021.
  36. ^ "Metric Act of 1866 – US Metric Association". usma.org. Retrieved 15 March 2021.
  37. ^ Taylor & Thompson 2003, p. 11.
  38. ^ Astin & Karo 1959.
  39. ^ Arnold Dieter (1991). Building in Egypt: pharaonic stone masonry. Oxford: Oxford University Press. ISBN 978-0-19-506350-9. p.251.
  40. ^ "Dictionary of the Scots Language". Archived from the original on 21 March 2012. Retrieved 6 August 2011.
  41. ^ The Penny Magazine of the Society for the Diffusion of Useful Knowledge. Charles Knight. 6 June 1840. pp. 221–22.
  42. ^ Hallock, William; Wade, Herbert T (1906). "Outlines of the evolution of weights and measures and the metric system". London: The Macmillan Company. pp. 66–69.
  43. ^ Cardarelli 2004.
  44. ^ Hofstad, Knut. "Mil". Store norske leksikon. Retrieved 18 October 2019.

References

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