SI Units (International System of Units)

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Note: Not all units below are SI units; some are “units outside the SI that are accepted for use with SI.”

Avoid obsolete symbols: Å, atm, cal, erg, kgf, Torr, ppm, gal, bar, µ, etc

Temperatures should be in °C or K (note the lack of a degree mark for K)

One metric ton (symbol “t”, sometimes referred to as “tonne”) is 1 t, 1 Mg, or 1000 kg

Density should be in kg/m3, not g/cm3

Force is always in Newtons (N), not kgf, and not kg (which is mass).

Liter symbol is “L”

Avoid the use of “cm” with one general exception–the diameter of trees is often given in cm

The use of “weight” should be avoided—use mass, for example, oven-dry mass

In ratios of unit symbols, note that the denominator should always be in the basic units (m, kg, s) without prefixes.  The exception is that kg is a basic SI unit so it comes with the prefix.


Author:  Frank Beall