The kilometre per hour (American English

American English

American English is a set of dialects of the English language used mostly in the United States. Approximately two-thirds of the world's native speakers of English live in the United States....

: kilometer per hour) is a unit of speed

Speed

In kinematics, the speed of an object is the magnitude of its velocity ; it is thus a scalar quantity. The average speed of an object in an interval of time is the distance traveled by the object divided by the duration of the interval; the instantaneous speed is the limit of the average speed as...

, expressing the number

Number

A number is a mathematical object used to count and measure. In mathematics, the definition of number has been extended over the years to include such numbers as zero, negative numbers, rational numbers, irrational numbers, and complex numbers....

 of kilometres traveled in one hour

Hour

The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...

. 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

Hour

The hour is a unit of measurement of time. In modern usage, an hour comprises 60 minutes, or 3,600 seconds...

, although the "hour", while not strictly an SI unit, is accepted for use with the International System of Units

International System of Units

The International System of Units is the modern form of the metric system and is generally a system of units of measurement devised around seven base units and the convenience of the number ten. The older metric system included several groups of units...

 by the International Bureau of Weights and Measures

International Bureau of Weights and Measures

The International Bureau of Weights and Measures , is an international standards organisation, one of three such organisations established to maintain the International System of Units under the terms of the Metre Convention...

 (BIPM).

In Australian and North American slang

Slang

Slang is the use of informal words and expressions that are not considered standard in the speaker's language or dialect but are considered more acceptable when used socially. Slang is often to be found in areas of the lexicon that refer to things considered taboo...

 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 kilometre

Kilometre

The kilometre is a unit of length in the metric system, equal to one thousand metres and is therefore exactly equal to the distance travelled by light in free space in of a second...

s.

Use of kph

The colloquial abbreviations "kph" and "kmph" are sometimes also used in English-speaking countries, in analogy to "miles per hour" (mph

MPH

MPH is a three-letter acronym that refers to miles per hour, a measurement of speedMPH may also refer to:* Make Poverty History, a campaign supported by Bob Geldof to end poverty in Africa...

), 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.

• Bulgarian Километър в час
• Dutch: kilometer per uur
• German: Kilometer pro Stunde
• Greek: χιλιόμετρα ανά ώρα / χιλιόμετρα την ώρα
• Italian: Chilometri all'ora
• Polish: kilometr na godzinę
• Portuguese: quilómetros por hora / quilômetro por hora
• Romanian:Kilometri pe oră
• Russian: Километр в час

In all cases, EU directives require the use of "km/h" in official documents in these languages. Similarly, US law requires the use of either "km/h" or "KM/H", but not "KPH" on speedometers.

Conversions

• 3.6 km/h ≡ 1 m/s, the SI unit of speed, metre per second
  Metre per second
  Metre per second is an SI derived unit of both speed and velocity , defined by distance in metres divided by time in seconds....
  
  
• 1 km/h ≈ 0.277 78 m/s
• 1 km/h ≈ 0.621 37 mph
  Miles per hour
  Miles per hour is an imperial unit of speed expressing the number of statute miles covered in one hour. It is currently the standard unit used for speed limits, and to express speeds generally, on roads in the United Kingdom and the United States. It is also often used to express the speed of...
  
   ≈ 0.911 34 feet per second
  Feet per second
  The foot per second is a unit of both speed and velocity . It expresses the distance in feet traveled or displaced, divided by the time in seconds...
  
  
• 1 knot ≡ 1.852 km/h (exactly)
• 1 mile per hour ≡ 1.609344 km/h (~1.61 km/h)