Kilometer - kilometre

The correct spelling in British English is kilometre. In American English, it is 'kilometer' (see also meter - metre).

The pronunciations also vary. The traditional British stress, which used to be preferred in academic circles, is on the first syllable, 'KILL-er-meet-er', IPA: /ˈkɪl ə miːt ə^r/. This appears to be being replaced by the normal American pronunciation with the stress on the second syllable, which has the vowel sound of 'got': 'kill-O-mitt-er', IPA: /kɪl ˈɒ mɪt ə^r/. In doubt, follow the preference of your teachers.

LPD records that where, in 1988, 52% of British speakers used the 'KILL-er-meet-er' pattern, by 1998, it was only 43%. 16% of American speakers in 1993 used this 'British' pronunciation. The note in LPD is instructive: On the analogy of ˈcentimetre, ˈmillimetre, it is clear that the stressing ˈkilometre [~KILL:-oh-meet-er] is logical and might be expected to predominate. Nevertheless, many people (particularly in the US, but also elsewhere) say kilˈom-. It might also be observed that in such other measures from the S.I. as kilogram and kilolitre, the stress is always on the first syllable; and the prefix kilo- is the same: 'KILL-oh' or 'KEEL-oh'. A further advantage in terms of consistency is that the second element in 'kilometre', the metre, sounds more like itself when the first syllable of KILL-oh-meet-er is stressed.

(OED adds that the variation is "prob[ably] under the influence of such words as speedometer, thermometer."

Kilo, as a free-standing word, is most often used as an abbreviation for 'kilogram'; but it has also been used for 'kilometre'. This latter use seems unnecessary: AWE recommends writers to avoid it.

The US military uses the abbreviation click for 'kilometer'.

See also Prefixes in units of measurement.