Definition
Milligram
A milligram is a mass unit equal to one thousandth of a gram.
What it means
Use milligrams for very small masses. The prefix milli- means one thousandth, so a gram is split into 1,000 equal milligrams. The symbol is mg, with lowercase m and lowercase g.
Remember it
One thousand milligrams stack up to one gram.
Example
A tiny paper label has a mass of 250 mg. Four labels have a total mass of 4 × 250 mg = 1,000 mg, which is exactly 1 g.
Watch for
A milligram measures mass, not liquid volume; mg and mL name different kinds of quantities.
Common mix-up
Do not change only the number or only the unit: the exact equivalence is 1 g = 1,000 mg.
Exact meaning
A milligram, symbol mg, is a unit of mass equal to 0.001 gram; therefore 1,000 milligrams equal 1 gram.