kilometre per hour

kilometre per hour

Unit whose name includes an SI unit and a non-SI unit accepted for use with SI
Name Symbol Quantity Value in SI units
kilometre per hour km/h speed 10003600 m s−1

Definition

The kilometre per hour, symbol km/h, is a non-SI unit of speed, accepted for use with the SI.
 
An object with a constant speed of one kilometre per hour moves a distance of one kilometre in one hour, or 10003600 metres in one second.

The kilometre per hour is derived from the metre (an SI base unit) and the hour (a non-SI unit accepted for use with the SI).

Distance ÷ Time = Speed Expressed in SI units
1 km ÷ 1 h = 1 km/h = 10003600 m s-1
3.6 km ÷ 1 h = 3.6 km/h = 36003600 m s-1
3600 m ÷ 3600 s = 36003600 m s-1 = 1 m s-1

A speed of 3.6 km/h is equal to 1 m s-1.

The kilometre per hour is the unit of speed used on road signs and motor vehicle speedometers in most countries of the world.


 
90 km/h   =   25 m s-1

Examples of motor vehicle speeds
Expressed in km/h Expressed in SI base units
18 km/h 5 m s-1
36 km/h 10 m s-1
54 km/h 15 m s-1
72 km/h 20 m s-1
90 km/h 25 m s-1
108 km/h 30 m s-1

Usage

Abreviations, such as kph and kmph, should not be used in place of the symbol km/h.