Kilometer works fine for everyday purposes, from fractions of it to orders of magnitude larger, i.e. both 0.1km and 7230km are understandable. Once you are in

Kilometer works fine for everyday purposes, from fractions of it to orders of magnitude larger, i.e. both 0.1km and 7230km are understandable. Once you are in the realm of science and engineering, you are more likely to encounter scientific notation anyways, e.g. 2.99 x 10^8 m instead of 299 Mm.