Kilometer (km)
Definition
One thousand meters (10³ m).
History
The kilometer, one thousand meters, was defined along with the metric system in the 1790s as its unit for long distances. It spread across the world with the metric system through the nineteenth and twentieth centuries.
Where it is used
Kilometers are the standard unit for road distances and running races in most of the world; the United States and United Kingdom still post road distances in miles.
Typical uses include road distances, running races.
Conversion pages
These pages convert kilometer to or from another unit in length.
Other Length units
Sources
- BIPM SI BIPM, The International System of Units (SI), 9th ed. (2019) · Dataset reviewed Nov 11, 2026