{{short description|Unit of length equal to 1,000 metres}} {{Redirect|km||KM (disambiguation){{!}}KM}} {{Use dmy dates|date=March 2023}} {{Use British English|date=September 2020}} {{Infobox unit | name = kilometre | image = 25 April Tagus bridge (10480970823).jpg | caption = The main span of the 25 de Abril Bridge in Lisbon, Portugal is {{convert|1.013|km|m}}. | symbol = km | standard = SI | quantity = length | units1 = SI base units | inunits1 = {{val|1000|ul=m}} | units2 = imperial/US&nbsp;units | inunits2 = ≈ {{val|0.62137|ul=mi}}<br /><!---->&emsp;≈ {{val|1093.6|ul=yd}}<br /><!---->&emsp;≈ {{val|3280.8|ul=ft}} | units3 = nautical&nbsp;units | inunits3 = ≈ {{convert|1|km|nmi|disp=out|lk=on|sigfig=5|comma=gaps}} }}

The '''kilometre''' (SI symbol: '''km'''; {{IPAc-en|ˈ|k|ɪ|l|ə|m|iː|t|ər}} or {{IPAc-en|k|ɪ|ˈ|l|ɒ|m|ə|t|ər}}), spelt<!-- no, "spelt" is not a mistake --> '''kilometer''' in American English, is a unit of length in the International System of Units (SI), equal to one thousand metres (kilo- being the SI prefix for {{val|1000}}). It is the preferred measurement unit to express distances between geographical places on land in most of the world; notable exceptions are the United States and the United Kingdom where the statute mile is used.

== Pronunciation== {{more citations needed section|date=October 2011}} There are two common pronunciations for the word.<ref>{{Citation |last=Jones |first=Daniel |author-link=Daniel Jones (phonetician) |title=English Pronouncing Dictionary |editor=Peter Roach |editor2=James Hartmann |editor3=Jane Setter |place=Cambridge |publisher=Cambridge University Press |orig-year=1917 |year=2003 |isbn=3-12-539683-2 }}</ref><!--Click the link for why /r/'s are included though they aren't phonemic in BrE, AusE, etc.--> # {{IPAc-en|ˈ|k|ɪ|l|ə|m|iː|t|ər|,_|-|l|oʊ|-}} # {{IPAc-en|k|ᵻ|ˈ|l|ɒ|m|ᵻ|t|ər}}

The first pronunciation follows a pattern in English whereby SI units are pronounced with the stress on the first syllable (as in kilogram, kilojoule and kilohertz) and the pronunciation of the actual base unit does not change irrespective of the prefix (as in centimetre, millimetre, nanometre and so on). It is generally preferred by the British Broadcasting Corporation (BBC), the Canadian Broadcasting Corporation (CBC), and the Australian Broadcasting Corporation (ABC).{{citation needed|date=February 2015}}

Many other users, particularly in countries where SI (the metric system) is not widely used, use the second pronunciation with stress on the second syllable.<ref>{{Cite news| url=http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/tv_and_radio/article3586220.ece | archive-url=https://web.archive.org/web/20110307091048/http://entertainment.timesonline.co.uk/tol/arts_and_entertainment/tv_and_radio/article3586220.ece | url-status=dead | archive-date=7 March 2011 | work=The Times | location=London | title=Correct pronunciation on the radio | first=Roland | last=White | date=23 March 2008 |access-date=7 May 2010}}</ref><ref>{{cite web|url=http://www.merriam-webster.com/dictionary/kilometer |title=Kilometer – Definition and More from the Free Merriam-Webster Dictionary |publisher=Merriam-Webster |access-date=2014-08-05}}</ref> The second pronunciation follows the stress pattern used for the names of measuring instruments (such as ''micrometer'', ''barometer'', ''thermometer'', ''tachometer,'' and ''speedometer''). The contrast is even more obvious in countries that use the American spelling of the word ''metre''. This pronunciation is irregular because it makes the kilometre the only SI unit with the stress on the second syllable.

After Australia introduced the metric system in 1970, the first pronunciation was declared official by the government's Metric Conversion Board. However, the Australian prime minister at the time, Gough Whitlam, insisted that the second pronunciation was the correct one because of the Greek origins of the two parts of the word.<ref>{{Cite web |url=http://www.cimms.ou.edu/~doswell/peeves/Discussions.html |title=E-mail Discussions on "Peeves" Topics |author=Charles A. Doswell III |website=Cooperative Institute for Mesoscale Meteorological Studies - University of Oklahoma |access-date=2014-08-05 |archive-url=https://web.archive.org/web/20081022055855/http://www.cimms.ou.edu/~doswell/peeves/Discussions.html |archive-date=2008-10-22 |url-status=dead}}</ref>

== Equivalence to other units of length == : {| |- | rowspan="8" style="vertical-align:top;"| 1 kilometre | ≡ | align=right | {{val|1000}} | metres |- | ≈ | align=right | {{val|3281}} |feet |- | ≈ | align=right | {{val|1094}} | yards |- | ≈ | align=right | 0.621 | miles |- | ≈ | align=right | 0.540 | nautical miles |- | ≈ | align=right | {{val|6.68|e=-9}} | astronomical units{{efn|One astronomical unit is defined as exactly {{val|149597870700|u=m}}.}} |- | ≈ | align=right | {{val|1.06|e=-13}} | light-years{{efn|A light-year is equal to {{val|9.4607304725808|e=12|u=km}} the distance light travels through vacuum in one year (365.25 days).}} |- | ≈ | align=right | {{val|3.24|e=-14}} | parsecs |}

== History == thumb|480px|right|Historical divisions of the meridian in France

By a decree on 8 May 1790, the French National Constituent Assembly ordered the French Academy of Sciences to develop a new measurement system. In August 1793, the French National Convention decreed the metre as the sole length measurement system in the French Republic and it was based on {{Sfrac|1|10}} millionth of the distance from the orbital poles (either North or South) to the Equator, this being a truly internationally based unit. The first name of the kilometre was "Millaire". Although the metre was formally defined in 1799, the myriametre ({{val|10000}}&nbsp;metres) was preferred to the "kilometre" for everyday use. The term "''myriamètre''" appeared a number of times in the text of Develey's book ''Physique d'Emile: ou, Principes de la science de la nature'',<ref>{{cite book |title = Physique d'Emile: ou, Principes de la science de la nature |volume = 1 |first1 = Emmanuel |last1 = Develey |year = 1802 |location = Paris |lang=fr |url = https://books.google.com/books?id=AFsIAAAAIAAJ&pg=PA90 }}</ref> (published in 1802), while the term ''kilometre'' only appeared in an appendix. French maps published in 1835 had scales showing ''myriametres'' and "''lieues de Poste''{{-"}} (Postal leagues of about {{val|4288}}&nbsp;metres).<ref>{{cite map |publisher = Laguillermie et Rambos |title = Map of the department of Hautes Pyrénées |year = 1835 |url= http://www.mereweather.net/hautespyrenees.htm |series = France Pittoresque |language= fr |access-date = 21 September 2012}}</ref>

The Dutch, on the other hand, adopted the kilometre in 1817 but gave it the local name of the ''mijl''.<ref>{{cite book |url = https://archive.org/details/allereerstegron00ramagoog |title = Allereerste Gronden der Cijferkunst |author = Jacob de Gelder |location = 's-Gravenhage and Amsterdam |language = nl |year = 1824 |pages = [https://archive.org/details/allereerstegron00ramagoog/page/n364 155]–156 |publisher = de Gebroeders van Cleef |trans-title=Introduction to Numeracy |access-date =2 March 2011}}</ref> It was only in 1867 that the term "''kilometer''{{-"}} became the only official unit of measure in the Netherlands to represent {{val|1000}}&nbsp;metres.<ref>{{Cite news |url= http://resources2.kb.nl/010285000/pdf/DDD_010287511.pdf |newspaper= De Locomotief. Nieuws, handels en Advertentie-blad |page= 2 |date= 12 August 1869 |title= [News from] Nederland |url-status= dead |archive-url= https://web.archive.org/web/20170227120542/http://resources2.kb.nl/010285000/pdf/DDD_010287511.pdf |archive-date = 27 February 2017}}</ref>

Two German textbooks dated 1842<ref name=Europa1842>{{cite web |url = http://home.fonline.de/fo0126//geschichte/groessen/mas1.htm |title = Amtliche Maßeinheiten in Europa 1842 |language = de |trans-title=Official units of measure in Europe 1842 |access-date = 26 March 2011}} Text version of Malaisé's book.</ref><ref>{{cite book |url = http://home.fonline.de/rs-ebs/geschichte/buch/titel.htm |title = Theoretisch-practischer Unterricht im Rechnen |language = de |trans-title=Theoretical and practical instruction in arithmetic |author = Ferdinand Malaisé |place = München |year = 1842 |pages = 307–322 |access-date = 26 March 2011}}</ref> and 1848<ref>{{cite book |url = http://commons.wikimedia.org/wiki/Category:Lehrbuch_des_gesammten_Rechnens_f%C3%BCr_die_vierte_Classe_der_Hauptschulen_in_den_k.k._Staaten_(Franz_Mozhnik) |first1 = Franz |last1 = Mozhnik |title = Lehrbuch des gesammten Rechnens für die vierte Classe der Hauptschulen in den k.k. Staaten. |language = de |trans-title=Arithmetic textbook for the fourth class in the [Austrian] Imperial and [Hungarian] Royal states |publisher = Im Verlage der k.k. Schulbücher Verschleiß-Administration |location = Vienna |year = 1848 |access-date = 19 July 2013 |at = Das Wegmaß}}</ref> respectively give a snapshot of the use of the kilometre across Europe: the kilometre was in use in the Netherlands and in Italy, and the myriametre was in use in France.

In 1935, the International Committee for Weights and Measures (CIPM) officially abolished the prefix "myria-" and with it the "myriametre", leaving the kilometre as the recognised unit of length for measurements of that magnitude.<ref>{{cite book |title = The Basis of Measurement – Volume 2 – Metrication and Current Practice. |first1 = Thomas |last1 = McGreevy |editor1-first = Peter |editor1-last = Cunningham |publisher = Picton |isbn = 0-948251-84-0 |year = 1997}}</ref>

The symbol '''km''' for the kilometre is in lower case and has been standardised by the BIPM.<ref>{{cite web |url=https://www.oxfordlearnersdictionaries.com/definition/english/kilometre?q=kilometre |title=Kilometre |website=Oxford Learner's Dictionaries |access-date=1 November 2019}}</ref><ref>{{cite web |title=The International System of Units (SI) |url=https://www.bipm.org/utils/common/pdf/si-brochure/SI-Brochure-9-EN.pdf#page=33 |publisher=International Bureau of Weights and Measures (BIPM) |access-date=8 January 2020 |pages=147–149 |date=2019}}</ref> A slang term for the kilometre in the US, UK, and Canadian militaries is ''klick''.<ref>{{cite web |title=MARINE CORPS JARGON |url=http://www.hqmc.marines.mil/Portals/143/Docs/Onboarding/Marine%20jargon.pdf |publisher=hqmc.marines.mil |access-date=3 March 2017}}</ref>

== See also == * Conversion of units, for comparison with other units of length * Cubic metre * Distance traveled * Metric prefix * Orders of magnitude (length) * Square kilometre

== Notes == {{Notelist}}

== References == {{Reflist}}

== External links == {{Spoken Wikipedia|kilometre.ogg|date=2013-06-27}} * {{commons category-inline|Distance indicators}}

{{SI units of length}}

Category:Metre +03 Category:1000 (number) Category:Units of length