Kilometers per hour - History & Background Information

What is Kilometers per hour?

 

The kilometre per hour (SI symbol: km/h; abbreviations: kph, kmph, km/hr) is a unit of speed, expressing the number of kilometres travelled in one hour.

1 km/h ≈ 0.27778 m/s
1 km/h ≈ 0.62137 mph ≈ 0.91134 ft/s
1 kn ≡ 1.852 km/h (exactly)
1 mph ≡ 1.609344 km/h

 

Symbol

 

The formal abbreviation for kilometres per hour is km/h.
Other abbreviations in use include kph and kmph, these are often used on car speedometers and probably came about as a metric equivalent of the mph abbreviation for miles per hour.

 

Alternative abbreviations in official use

 

km/j or km/jam (Indonesia and Malaysia)
km/t or km/tim (Norway, Denmark and Sweden; also use km/h)
kmph (Sri Lanka and India)
กม./ชม. (Thailand; also uses km/hr)
كم/س or كم/ساعة (Arabic-speaking countries, also use km/h)
קמ"ש (Israel)
 

History

 

Abbreviations for "kilometres per hour" did not appear in the English language until the late nineteenth century.

The kilometre, a unit of length, first appeared in English in 1810,and the compound unit of speed "kilometers per hour" was in use in the US by 1866.

Kilometres per hour came into common usage sometime during the mid 19th century, during the time of the expansion of the railways and have been widely adopted especially in regard to speed for automobiles. 

With the introduction of SI units in 1960 the standard abbreviations were formalised, though adoption of these is still not 100%.

In 1975 a European Union directive required the use of the km/h abbreviation on all speedometers on cars sold within the EU.

 

Usage 

 

Kilometres per hour is the most commonly seen metric unit of speed, being used for road speed limit signs in most countries in the world. Although technically a derivative unit, its usefulness as a term for the speed of motor vehicles has perpetuated its widespread use.

Internationally, km/h is the most commonly used unit of speed on traffic signs and road vehicle speedometers.