# Kilometre

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1 kilometre =

The kilometre (American spelling: kilometer), symbol km[1] is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in 1299 792.458 of a second.[2] It is the conventionally used measurement unit for expressing distances between geographical places in most of the world; notable exceptions are the United States and the United Kingdom where the statute mile is used.

A slang term for the kilometre in the military is klick and in common speech involving distance it is often abbreviated as simply a k (kay).[3][4] [5] [6]

## Pronunciation

There are two pronunciations for the word:

The former pronunciation follows the general pattern in English whereby metric units of measurement are pronounced with the stress on the first syllable, and preserves the pronunciation of metre. It is generally preferred by the BBC, while most scientists use the pronunciation with stress on the second syllable.[7][8] The latter pronunciation, which follows the stress pattern used for the names of measuring instruments (such as micrometer, barometer, thermometer, tachometer and speedometer), is in common usage as well.

When Australia introduced the metric system, 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.[9]

## Equivalence to other units of length

 1 kilometre = 1000 metres ≈ 0.621 statute miles[10] ≈ 1094 yards[11] ≈ 3,281 feet[12] ≈ 0.540 nautical miles[13] ≈ 6.68×10 astronomical units[14] ≈ 1.057×10 light-years[15] ≈ 3.24×10 parsecs

## Visualisation

The kilometre may be visualized in terms of prominent landmarks.

### Niagara Falls (1039 m)

 The distance between the American extremity of the Niagara Falls and the Canadian extremity is 1039 m,[16] or fractionally over 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. ```NE extremity of American Falls SW extremity of the Horseshoe Falls ```

### The Mall, London (987 m)

 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. 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.[16] The picture on the right is taken from about halfway down The Mall. ```Centre of the Victoria Memorial Entrance to the Admiralty Arch ```

### Kowloon – Hong Kong Crossing (1007 m)

 Hong Kong Harbour boasts one of the busiest waterways in the world. Until 1970 the only way to cross the harbour was the Star Ferry which had terminals on the Kowloon peninsular and the island of Hong Kong itself. The distance that the ferry travels, as measured from passenger entrance to passenger entrance is 1007 m.[16] ```Hong Kong (Central Star Ferry Pier) Kowloon (Tsim Sha Tsui Star Ferry Pier) ```

### Suspension bridges

 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 Third 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 linking England and Wales

## International usage

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

### United Kingdom

Although road signs in the United Kingdom show distances in miles,[17][18] location marker posts that are used for reference purposes by road engineers and emergency services are kilometre-based.[19] The advent of the mobile phone has been instrumental in the English Department for Transport authorising the use of driver location signs to convey the [kilometre-based] information of location marker posts to road users should they need to contact the emergency services.

### United States

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.[20] However, 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.)

## Notes and references

1. For the purposes of compatibility with Chinese, Japanese and Korean characters there is a Unicode symbol for the kilometre, ㎞, (code 339E).
2. . Bureau International des Poids et Mesures. Retrieved 2009-06-22.
3. Walshe, Cathy (18 August 2008). . The New Zealand Herald. Retrieved 2008-10-27. "The race was four laps, and I was just counting down the k's to the end"
4. Kuschke, Jazz (21 August 2007). . Getaway Magazine via iafrica.com. Retrieved 2008-10-27. "yet less than 10 kays down the road"
5. . Enjoy Darwin. Retrieved 2008-10-27. "Camooweal just over the Queensland border a further 250 k's along the road"
6. These non-standard terms can also refer to kilometres per hour.
7. White, Roland (2008-03-23). . The Times (London). Retrieved 2010-05-07.
8. http://www.merriam-webster.com/dictionary/kilometer
9. http://www.cimms.ou.edu/~doswell/peeves/Discussions.html
10. One international statute mile is exactly 1.609344 kilometres.
the rule-of-thumb "multiply by 8 and divide by 5" gives a conversion of 1.6, which is approximately 0.6% too low.
11. One international yard is exactly 0.0009144 kilometres.
12. One international foot is exactly 0.0003048 kilometres.
13. One nautical mile is equal to 1.852 kilometres.
14. One astronomical unit is currently accepted to be equal to 149,597,870,691 ± 30 metres.
15. A light-year is equal to 9,460,730,472,580.8 kilometres, the distance light travels through vacuum in one Julian year of 365.25 days.
16. a b c Measured on Google Earth – accessed 2010-02-10
17. . 2002-12-16. Retrieved 2010-01-12.
18. The Council of the European Communities (2009-05-27). . Retrieved 2010-01-12.
19. Hansard. . Retrieved 2009-11-04.
20. . US Department of Transport. Retrieved 2007-10-12.