Grain: A grain is a unit of measurement of mass, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single virtual ideal seed of a cereal.
- Grain used to measure mass of bullets and propellants.
- In Archery, the grain is the SI unit used to weight arrows
- In dentistry, gold foil is used as material to restore teeth where measurement is done in grains.
- In North America, grains per US gallon(gpg)of calcium carbonate equivalents measures the hardness of water. One grain per US gallon is approximately 17.1 ppm. Soft water contains 1–4 gpg of calcium carbonate equivalents, while hard water contains 11–20 gpg.
- To prescribe older medicines as aspire measured in grain.
- In the US, to measure emission level and moisture.