Engineering Statics/Appendices/SI Units Used in Mechanics

Selected Rules for Writing Metric Quantities

 * For readability, use unit prefixes such that the number is between 0.1 and 1000.
 * The most common prefixes in engineering are giga, mega, kilo, centi, milli, and micro. Prefixes like hecto, deka, and deci make for awkward numbers.
 * Unit combinations should only use prefixes in the numerator (write kJ/s instead of J/ms), with the exception of kg.
 * Do not double up the prefixes, e.g. write GW not kMW.
 * Use a dot to multiply units (write N•m not Nm)
 * Avoid the ambiguity of multiple divisions (write N/m3 not N/m/m/m)
 * Exponents refer to the entire unit symbol (mm2 means (mm)2)
 * Use spaces instead of commas to make long numbers easier to read (e.g. 1 210 000 000.001 W), ignore for numbers of four digits.