Kilometer

A kilometre (American spelling: kilometer, symbol km) is a unit of length in the metric system, equal to one thousand metres, the current SI base unit of length. It can be written in scientific notations as 1&times;10³ m (engineering notation) or 1 E+3 m (exponential notation) — both meaning 1,000 &times; 1 m.

A corresponding unit of area is the square kilometre and a corresponding unit of volume is the cubic kilometre.

Although, in English, metric units of measurement are usually pronounced with the stress on the first syllable, as in /ˈkɪl.əˌmiː.tə(r)/, pronunciation of the word "kilometre" with the stress on the second syllable /kɪˈlɒm.ə.tə(r)/ is in common usage (see List of words of disputed pronunciation). The latter pronunciation follows the stress pattern used for the names of measuring instruments, such as barometer, thermometer, tachometer and speedometer. This stress pattern is not commonly used for other metric measurements such as millimetre or centimetre.

Slang terms for kilometre include "click" (sometimes spelled "klick" or "klik") and "kay" (or "k"). These non-standard terms can also refer to kilometres per hour, which itself is abbreviated as km/h, km h-1, km·h-1 or, informally, kph.

"Kilometrage" may be used in the same way as "mileage".

Equivalence to other units of length
1 kilometre is equal to:
 * 1,000 metres (1 metre is equal to 0.001 kilometres)
 * about 0.621 statute miles (1 statute mile is equal to 1.609344 kilometres)
 * the formula "multiply by 5 and divide by 8" gives a conversion of 0.625, accurate to 0.6%, which is a useful approximation
 * about 1,094 international yards (1 international yard is equal to 0.0009144 kilometres)
 * about 3,281 feet (1 foot is equal to 0.0003048 kilometres)
 * exactly 0.00000000000010570008340246153 Light Years (1 light year is equal to about 9.5 trillion kilometers)

International usage
The United Kingdom and the United States are the only two developed countries that have not changed their road signs from miles to kilometres.

Although the UK has officially adopted the metric system, there is no intention to replace the mile on road signs in the near future, owing to the British public's attachment to traditional imperial units of distance, i.e., miles, yards and inches, and the cost of changing speed signs (which could not be replaced during general maintenance, like distance signs, for safety reasons). As of 11 September 2007, the EU has allowed Britain to continue using the imperial systems. EU commissioner Günter Verheugen said: "There is not now and never will be any requirement to drop imperial measurements."

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. However, the Manual on Uniform Traffic Control Devices since 2000 published in both metric and American Customary Units. (See also Metrication in the United States.)

Unicode symbols
For the purposes of compatibility with Chinese, Japanese and Korean (CJK) characters, Unicode has symbols for:
 * kilometre (㎞) - code 339E
 * square kilometre (㎢) - code 33A2
 * cubic kilometre (㎦) - code 33A6