The milligram (symbol mg) is an SI unit of mass. It is defined as:
1 mg = 10−6 kg = 1/1,000,000 (one millionth) of a kilogram.
A thousand of them make up a gram; a million make a kilogram; a billion make a metric tonne.
The milligram is useful for stating the masses of small objects. A grain of sand might be close in mass to a milligram. Laboratory scientists frequently measure masses in milligrams. Substances found in small amounts, such as sodium in food, and doses of pharmaceuticals, such as aspirin, are generally measured in milligrams.
One milligram is the weight of 1 mm3 of water (a cube of size 1 mm x 1 mm x 1 mm).
See 1 E-6 kg for comparisons.
microgram << milligram << centigram