The kilometre per hour (American English: kilometer per hour) is a unit of speed, expressing the number of kilometres traveled in one hour. The unit symbol is km/h or km·h−1.
Worldwide, the km/h is the most commonly used speed unit on road signs and car speedometers. Along with the kW·h, km/h is the most commonly used metric unit based on the hour, although the "hour", while not strictly an SI unit, is accepted for use with the International System of Units by the International Bureau of Weights and Measures (BIPM).[2]
In Australian and North American slang and military usage, km/h is commonly pronounced, and sometimes even written, as klicks or kays (K's), although these may also be used to refer to kilometres.
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The colloquial abbreviations "kph" and "kmph" are sometimes also used in English-speaking countries, in analogy to "miles per hour" (mph), even though the official recommendation from the BIPM is to use "km/h". The symbol (as opposed to abbreviation) is in near-universal use elsewhere, even though the letters "km" and "h" do not always correspond to "kilometres" or "hours" in the language concerned.
The following are translations of the text "kilometres per hour" where either "km" or "h" do not appear in the text.[3]
In all cases, EU directives require the use of "km/h" in official documents in these languages.[4] Similarly, US law requires the use of either "km/h" or "KM/H", but not "KPH" on speedometers.[5]
| m/s | km/h | mph | knot | ft/s | |
|---|---|---|---|---|---|
| 1 m/s = | 1 | 3.6 | 2.236936 | 1.943844 | 3.280840 |
| 1 km/h = | 0.277778 | 1 | 0.621371 | 0.539957 | 0.911344 |
| 1 mph = | 0.44704 | 1.609344 | 1 | 0.868976 | 1.466667 |
| 1 knot = | 0.514444 | 1.852 | 1.150779 | 1 | 1.687810 |
| 1 ft/s = | 0.3048 | 1.09728 | 0.681818 | 0.592484 | 1 |
(Values in bold face are exact.)