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"km" redirects here. For other uses, see KM (disambiguation).
Unit systemSI
Unit oflength
Unit conversions
1 km in ...... is equal to ...
   SI   1000 m
   imperial or   0.6213mi
   US units   3280.8 ft

The kilometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: km) or kilometer (American spelling) is a unit of length in the metric system, equal to one thousand metres (kilo- being the SI prefix for 1000). It is now the measurement unit used officially for expressing 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 the official unit used.

k (pronounced kay) is occasionally used in some English-speaking countries as an alternative for the word kilometre in colloquial writing and speech.[1][2][3] A slang term for the kilometre in the US military is klick.[4]


There are two common pronunciations for the word:

The former pronunciation follows the general pattern in English whereby metric units are pronounced with the stress on the first syllable, and the pronunciation of the actual base unit does not change irrespective of the prefix. It is generally preferred by the British Broadcasting Corporation (BBC) and the Australian Broadcasting Corporation (ABC).

Many scientists and other users, particularly in countries where the metric system is not widely used, use the pronunciation with stress on the second syllable.[5][6] The latter pronunciation follows the stress pattern used for the names of measuring instruments (such as micrometer, barometer, thermometer, tachometer and speedometer). The problem with this reasoning, however,[citation needed] is that the word meter in those usages refers to a measuring device, not a unit of length. The contrast is even more obvious in countries using the English rather than American spelling of the word metre.

When Australia introduced the metric system in 1975, 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.[7]

Equivalence to other units of length[edit]

1 kilometre1000metres
0.540nautical miles
6.68×10−9astronomical units[8]


Although the metre was formally defined in 1799, the myriametre (10,000 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,[10] (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 4288 metres)[11]

The Dutch on the other hand adopted the kilometre in 1817 but gave it the local name of the mijl.[12] It was only in 1867 that the term "kilometer" became the only official unit of measure in the Netherlands to represent 1000 metres.[13]

Two German textbooks dated 1842[14][15] and 1848[16] 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.[17]


The kilometre may be visualised in terms of prominent landmarks.

Niagara Falls[edit]

Niagara Falls from Prospect Point. The extremity of the Horseshoe Falls in the distance is about one kilometre away

The distance between the American extremity of the Niagara Falls and the Canadian extremity is 1039 m,[18] or slightly more than a kilometre. Although the length of the rim of the Canadian extremity (Horseshoe Falls) is quoted as being 790 m and the rim of the American extremity American Falls as being 320 m which add up to more than 1110 m, the rim of the Horseshoe falls is far from straight, so the direct distance between the end-points is 304 m.

43°05′08″N 79°04′08″W / 43.08557°N 79.06885°W / 43.08557; -79.06885 NE extremity of American Falls (Prospect Point)
43°04′44″N 79°04′41″W / 43.07901°N 79.07798°W / 43.07901; -79.07798 SW extremity of the Horseshoe Falls

The Mall, London[edit]

The Mall from Buckingham Palace on the occasion of the Queen's golden jubilee. The Victoria Memorial is in the foreground and the Admiralty Arch in the distance is about one kilometre away.

The Mall, which leads up to Buckingham Palace, is one of London's main tourist attractions. Immediately in front of the palace is the Victoria Memorial, erected in memory of Queen Victoria (foreground of the picture to the right). At the opposite end is the Admiralty Arch which links The Mall to Trafalgar Square. The distance from the entrance to the Admiralty Arch to the centre of the Victoria Memorial is 987 m.[18]

51°30′07″N 0°08′26″W / 51.50185°N 0.14064°W / 51.50185; -0.14064 Centre of the Victoria Memorial
51°30′24″N 0°07′44″W / 51.50671°N 0.12876°W / 51.50671; -0.12876 Entrance to the Admiralty Arch

Kowloon – Hong Kong Crossing[edit]

Hong Kong – Tsim Sha Tsui Pier. The ferry terminal on the Kowloon Peninsular, visible in the centre of the picture, is about a kilometre from the Central Ferry Pier.

The Victoria Harbour separates two major areas of Hong KongKowloon and Hong Kong Island. Until 1970 the only way to cross the harbour was the Star Ferry, which had terminals on both sides. The distance that the ferry travels, as measured from passenger entrance to passenger entrance is 1007 m.[18]

22°17′13″N 114°09′41″E / 22.28707°N 114.16133°E / 22.28707; 114.16133 Hong Kong (Central Star Ferry Pier)
22°17′37″N 114°10′05″E / 22.29371°N 114.16803°E / 22.29371; 114.16803 Kowloon (Tsim Sha Tsui Star Ferry Pier)

Central Park, Manhatta, New York City[edit]

Central Park in New York City is 849 metres wide. It extends (roughly east and west) from Fifth Avenue to Eighth Avenue (also known as Central Park West). The distance between Eighth Avenue and Madison Avenue (one block east of Fifth Avenue) is 1011 metres. The width of the park is visible from many nearby skyscrapers and is walked daily by many people. It is approximately 4 kilometres in length (from north to south).

The width of Central Park is visible from many buildings in Manhattan, and the park is walked regularly by many residents and visitors.

Suspension bridges[edit]

The Tagus Bridge in Lisbon, Portugal has a central span of 1.013 km

A number of suspension bridges have a central span of a kilometre or more. The George Washington Bridge in New York (central span 1067 m) was the first bridge in the world to have a span of more than a kilometre and between 1931 and 1937, had the longest span of any bridge in the world. Other bridges that have a central span of about one kilometre include:

1030 m Third Kurushima-Kaikyo Bridge in Japan
1020 m Second Kurushima-Kaikyo Bridge in Japan
1013 m Ponte 25 de Abril (Tagus Bridge) in Lisbon, Portugal
1006 m Forth Road Bridge in Scotland
990 m Kita Bisan-Seto Bridge (Great Seto Bridge) in Japan
988 m Severn Bridge, England, leading up to the Welsh border.

International usage[edit]

Chinese expressway distances road sign in eastern Beijing. Although the primary text is in Chinese, the distances use internationally recognised characters.

The United Kingdom and the United States are the only two developed countries which continue to use miles on road signs.[19]

United Kingdom[edit]

In the United Kingdom, road signs show distances in miles[20][21] and location marker posts that are used for reference purposes by road engineers and emergency services show distance references in unspecified units which are kilometre-based.[22] The advent of the mobile phone has been instrumental in the British Department for Transport authorising the use of driver location signs to convey the distance reference information of location marker posts to road users should they need to contact the emergency services.

United States[edit]

In the US, the National Highway System Designation Act of 1995 prohibits the use of federal-aid highway funds to convert existing signs or purchase new signs with metric units.[23] The Executive Director of the US Federal Highway Administration, Jeffrey Paniati, wrote in a 2008 memo: "Section 205(c)(2) of the National Highway System (NHS) Designation Act of 1995 prohibited us from requiring any State DOT [Department of Transport] to use the metric system during project development activities. Although the State DOT's had the option of using metric measurements or dual units (metrics/inch-pounds), all of them abandoned metric measurements and reverted to sole use of inch-pound values."[24] The Manual on Uniform Traffic Control Devices since 2000 is published in both metric and American Customary Units. (See also Metrication in the United States.)

Covering one kilometre[edit]

The time taken to cover a kilometre is dependent on one's speed. Walking on flat ground, a hiker can expect to cover one kilometre in 12 minutes[25] while a car travelling at a speed of 120 kilometres per hour (75 mph)—the speed limit on numerous European expressways—will cover a kilometre in 30 seconds.

Some sporting disciplines feature 1000 m (one-kilometre) races in major events (such as the Olympic Games), but in other disciplines, even though world records are catalogued, the one kilometre event remains a minority event. The world records for various sporting disciplines are:

Running (M)Noah Ngeny2:11.96[26]Rieti, Italy5 Sep 1999Not an Olympic event
Running (F)Svetlana Masterkova2:28.98[27]Brussels23 Aug 1996Not an Olympic event
Speed Skating (M)Shani Davis1:06.42[28]Salt Lake City7 Mar 2009
Speed Skating (F)Cindy Klaasen1:13.11[28]Calgary25 Mar 2006
Cycling (M)Arnaud Tourant58.875 s[29]La Paz, Bolivia10 Oct 2001No official 1000 m woman's record

See also[edit]

Notes and references[edit]

  1. ^ Walshe, Cathy (18 August 2008). "Triathlon: Hewitt bubbling after top 10 finish". The New Zealand Herald. Retrieved 27 October 2008. "The race was four laps, and I was just counting down the k's to the end" 
  2. ^ Kuschke, Jazz (21 August 2007). "The great north (off) road". Getaway Magazine via Retrieved 27 October 2008. "yet less than 10 kays down the road" 
  3. ^ "Traveling the Roads to Darwin". Enjoy Darwin. Retrieved 27 October 2008. "Camooweal just over the Queensland border a further 250 k's along the road" 
  4. ^ Rod Powers. "How Far is a "Klick" in the Military?". Archived from the original on 13 April 2010. Retrieved 13 April 2010. 
  5. ^ White, Roland (23 March 2008). "Correct pronunciation on the radio". The Times (London). Retrieved 7 May 2010. 
  6. ^ "Kilometer - Definition and More from the Free Merriam-Webster Dictionary". Retrieved 2014-08-05. 
  7. ^ "damage lessons". Retrieved 2014-08-05. 
  8. ^ One astronomical unit is currently accepted to be equal to 149597870691±30 m.
  9. ^ A light-year is equal to 9.4607304725808×1012 km the distance light travels through vacuum in one year (365.25 days).
  10. ^ Develey, Emmanuel (1802). Physique d'Emile: ou, Principes de la science de la nature 1. Paris. 
  11. ^ Laguillermie et Rambos (1835) (in French). Map of the department of Hautes Pyrénées (Map). France Pittoresque. Retrieved 21 September 2012.
  12. ^ Jacob de Gelder (1824). Allereerste Gronden der Cijferkunst [Introduction to Numeracy] (in Dutch). 's Gravenhage and Amsterdam: de Gebroeders van Cleef. pp. 155–156. Retrieved 2 March 2011. 
  13. ^ "[News from] Nederland". De Locomotief. Nieuws, handels en Advertentie-blad. 12 August 1869. p. 2. 
  14. ^ "Amtliche Maßeinheiten in Europa 1842" [Official units of measure in Europe 1842] (in German). Retrieved 26 March 2011Text version of Malaisé's book 
  15. ^ Ferdinand Malaisé (1842). Theoretisch-practischer Unterricht im Rechnen [Theoritcal and practical instruction in arithmetic] (in German). München. pp. 307–322. Retrieved 26 March 2011. 
  16. ^ Mozhnik, Franz (1848). Lehrbuch des gesammten Rechnens für die vierte Classe der Hauptschulen in den k.k. Staaten. [Arithmetic textbook for the fourth class in the [Austrian] Imperial and [Hungarian] Royal states] (in German). Vienna: Im Verlage der k.k. Schulbücher Verschleiß-Administration. Das Wegmaß. Retrieved 19 July 2013. 
  17. ^ McGreevy, Thomas (1997). Cunningham, Peter, ed. The Basis of Measurement - Volume 2 - Metrication and Current Practice. Picton. ISBN 0-948251-84-0. 
  18. ^ a b c Measured on Google Earth – accessed 2010-02-10
  19. ^ "Appendix G :: Weights and measures". The World Factbook. Central Intelligence Agency. Retrieved 24 May 2012. 
  20. ^ "Statutory Instrument 2002 No. 3113 - The Traffic Signs Regulations and General Directions". 16 December 2002. Retrieved 12 January 2010. 
  21. ^ The Council of the European Communities (27 May 2009). "Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC". Retrieved 12 January 2010. 
  22. ^ Hansard. "21 October 2009 : Column 1446W". Retrieved 4 November 2009. 
  23. ^ "50th Anniversary of the Interstate Highway System - Frequently Asked Questions". US Department of Transport. Retrieved 12 October 2007. 
  24. ^ Update on Metric Use Requirements for FHWA Documents US Department of Transportation, Federal Highway Administration, 25 November 2008.
  25. ^ "Estimating Distance Travelled". Walkhighlands Scotland. Retrieved 9 November 2011.  thus with a speed of 5 kilometres per hour (3 mph)
  26. ^ "Men's World Records". Track and Field. Retrieved 9 November 2011. 
  27. ^ "Women's World Records". Track and Field. Retrieved 9 November 2011. 
  28. ^ a b "Speed Skating: Complete history list of World Records recognized by ISU". International Skating Union. 1 July 2009. Retrieved 9 November 2011. 
  29. ^ "Track Records". Union Cycliste Internationale. Retrieved 9 November 2011.