Kilo officially means 1000, not 1024.

To resolve the confusion with 1024 in data processing, in December 1998 the International Electrotechnical Commission created new prefixes for binary multiples (q.v. for fuller explanation).

In brief: kibi is 1024, mebi is 1 048 576, then gibi, tebi, pebi, ebi. Their symbols have a capital letter then i: thus KiB = kibibyte, MiB, GiB etc.