Kilometer per Hour (km/h)
Definition
Kilometers per hour (symbol km/h, sometimes kph) is a metric unit of speed equal to exactly 1/3.6 meters per second. It is the standard road-speed unit on speedometers and traffic signs in most countries that use the metric system.
History
Kilometers per hour came into widespread use with metric road signage during the 20th century, replacing local distance-per-time units in most of Europe and Latin America. The 1968 Vienna Convention on Road Signs and Signals helped standardize signage internationally, and km/h became the default on Vienna-Convention signage.
Despite being convenient for road use, km/h is not an SI base or derived unit; the SI unit of speed is the meter per second (m/s). The kilometer per hour is accepted for use with the SI, however, and most modern vehicle speedometers display both km/h and mph.
Standard reference
Defined as 1 km / 1 h = 1,000 m / 3,600 s = 1/3.6 m/s exactly. Listed in NIST Special Publication 811; included in the 1968 Vienna Convention on Road Signs and Signals.
Common conversions
| 1 km/h | = 0.621371 mph |
|---|---|
| = 0.277778 m/s | |
| = 0.911344 ft/s | |
| = 0.539957 kn |