[7] 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".

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,[29] In contrast to the "symbols" designated for use with the SI system, news organisations such as Reuters[30] and The Economist[31] require "kph".

At the same time the CGPM formalised the rules for combining units – quotients could be written in one of three formats resulting in "km/h", "km h−1" and "km·h−1" being valid representations of "kilometres per hour".

[34] M. Danloux-Dumesnils[35] provides the following justification for this distinction: It has already been stated that, according to Maxwell, when we write down the result of a measurement, the numerical value multiplies the unit.

Another EU directive, published in 1975, regulates the layout of speedometers within the European Union, and requires the text "km/h" in all languages,[43] even where that is not the natural abbreviation for the local version of "kilometres per hour".

[44] However, the Federal Motor Vehicle Safety Standard number 101 ("Controls and Displays") allows "any combination of upper- and lowercase letters" to represent the units.