The kilometre ( SI symbol: km; or ), spelt kilometer in

American English American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances i ...

, is a

unit of length A unit of length refers to any arbitrarily chosen and accepted reference standard for measurement of length. The most common units in modern use are the metric units, used in every country globally. In the United States the U.S. customary unit ...

in the

International System of Units The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. E ...

(SI), equal to one thousand

metre The metre ( British spelling) or meter ( American spelling; see spelling differences) (from the French unit , from the Greek noun , "measure"), symbol m, is the primary unit of length in the International System of Units (SI), though its pr ...

s (

kilo- Kilo is a decimal unit prefix in the metric system denoting multiplication by one thousand (103). It is used in the International System of Units, where it has the symbol k, in lowercase. The prefix ''kilo'' is derived from the Greek word () ...

being the

SI prefix The International System of Units, known by the international abbreviation SI in all languages and sometimes pleonastically as the SI system, is the modern form of the metric system and the world's most widely used system of measurement. ...

for ). It is now the measurement unit used 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 The mile, sometimes the international mile or statute mile to distinguish it from other miles, is a British imperial unit and United States customary unit of distance; both are based on the older English unit of length equal to 5,280 English ...

is the unit used. The abbreviations k or K (pronounced ) are commonly used to represent kilometre, but are not recommended by the BIPM. A slang term for the kilometre in the US, UK, and Canadian militaries is ''

klick Click, Klick and Klik may refer to: Airlines * Click Airways, a UAE airline * Clickair, a Spanish airline * MexicanaClick, a Mexican airline Art, entertainment, and media Fictional characters * Klick (fictional species), an alien race in t ...

''.

Pronunciation

There are two common pronunciations for the word. # # The first pronunciation follows a pattern in English whereby metric units are pronounced with the stress on the first syllable (as in

kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially ...

, kilojoule and

kilohertz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

) and the pronunciation of the actual base unit does not change irrespective of the prefix (as in centimetre, millimetre,

nanometre 330px, Different lengths as in respect to the molecular scale. The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American and British English spelling differences#-re, ...

and so on). It is generally preferred by the British Broadcasting Corporation (BBC), the Canadian Broadcasting Corporation (CBC), and the Australian Broadcasting Corporation (ABC). Many other users, particularly in countries where the metric system is not widely used, use the second pronunciation with stress on the second syllable. 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 which use the Commonwealth spelling rather than American spelling of the word ''metre''. This pronunciation is irregular because this makes the kilometre the only SI unit in which the stress is on the second syllable. 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.

Equivalence to other units of length

History

By a decree of 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 The National Convention (french: link=no, Convention nationale) was the parliament of the Kingdom of France for one day and the French First Republic for the rest of its existence during the French Revolution, following the two-year National ...

decreed the

as the sole length measurement system in the French Republic and it was based on millionth of the distance from the

orbital pole An orbital pole is either point at the ends of an imaginary line segment that runs through the center of an orbit (of a revolving body like a planet, moon or satellite) and is perpendicular to the orbital plane. Projected onto the celestial sphe ...

s (either North or South) to the

Equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can a ...

, 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 The following are examples of orders of magnitude for different lengths. __TOC__ Overview Detailed list To help compare different orders of magnitude, the following list describes various lengths between 1.6 \times 10^ metres and 10 ...

( 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'', (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 metres). The Dutch, on the other hand, adopted the kilometre in 1817 but gave it the local name of the ''mijl''. It was only in 1867 that the term "''kilometer'' became the only official unit of measure in the Netherlands to represent metres. Two German textbooks dated 1842 and 1848 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.

Kilometre records

Some sporting disciplines feature (one-kilometre) races in major events (such as the Olympic Games). In some disciplines—although world records are catalogued—one-kilometre events remain a minority.

References

External links