, using "km/h." The SI representations, classified as symbols, are "km/h", "" and "". Several other abbreviations of "kilometres per hour" have been used since the term was introduced and many are still in use today; for example, dictionaries list "kph", "kmph" and "km/hr" as English abbreviations. While these forms remain widely used, the International Bureau of Weights and Measures uses "km/h" in describing the definition and use of the International System of Units. The entries for "kph" and "kmph" in the ''
Oxford Advanced Learner's Dictionary'' state that "the correct scientific unit is km/h and this is the generally preferred form".
Abbreviations 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" did not begin to be abbreviated in print until many years later, with several different abbreviations existing near-contemporaneously. With no central authority to dictate the rules for abbreviations, various publishing houses and standards bodies have their own rules that dictate whether to use upper-case letters, lower-case letters, periods and so on, reflecting both changes in fashion and the image of the publishing house concerned, In contrast to the "symbols" designated for use with the SI system, news organisations such as
Reuters and
The Economist require "kph". In informal Australian usage, km/h is more commonly pronounced "kays" or "kays an hour". In military usage, "klicks" is used, though written as km/h.
Unit symbols In 1879, four years after the signing of the
Treaty of the Metre, the
International Committee for Weights and Measures (CIPM) proposed a range of symbols for the various metric units then under the auspices of the
General Conference on Weights and Measures (CGPM). Among these were the use of the symbol "km" for "kilometre". In 1948, as part of its preparatory work for the
SI, the CGPM adopted symbols for many units of measure that did not have universally agreed symbols, one of which was the symbol "h" for "hours". At the same time the CGPM formalised the rules for combining units quotients could be written in one of three formats resulting in , and being valid representations of "kilometres per hour". The SI standards, which were
MKS-based rather than
CGS-based, were published in 1960 and have since then have been adopted by many authorities around the globe including academic publishers and legal authorities. The SI explicitly states that unit symbols are not abbreviations and are to be written using a very specific set of rules. provides the following justification for this distinction: SI, and hence the use of (or or ) has now been adopted around the world in many areas related to health and safety and in
metrology in addition to the SI unit
metres per second (, or ). SI is also the preferred system of measure in academia and in education.
Non-SI 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) •
км/ч (Russia and Belarus in a Russian-language context) •
км/г (Belarus in a Belarusian-language context) •
км/год (Ukraine) •
km/st (Azerbaijan) •
km/godz (Poland) == Regulatory use ==