Do all SI symbols require a preceding space?
The only exceptions are the percent symbol (25%) and the symbols of planar angle (45° 10′ 30″). In academic texts, you might also see a space before the percent symbol, but never in a technical or business document. In the dim, distant past, some engineers were taught to omit the space before a single-character symbol like m for metre, but that’s definitely incorrect.
The space is more than just a convention: it is a requirement of the international and Australian standards that govern the use of SI symbols.
There is no such requirement, however, for the abbreviations of imperial units of measure, but for consistency, we treat imperial abbreviations (such as in., psi, and lb) as if they were symbols, with the intervening space. Also, use a non-breaking space (Ctrl+Shift+Space in Microsoft Word) so the symbol is never orphaned from its number at the end of a line.
See the topic on symbols in the style guide for the complete set of rules.
October 8, 2015 / Tim McAuley / 0