 Grain (unit)

A grain (unit) is a unit of mass equal to exactly $64.79891\mathrm{mg}$, or $0.00006479891\mathrm{kg}$. Thus a recorded mass of ten grains converts to $647.9891\mathrm{mg}$. The abbreviation is $\mathrm{gr}$; it must be distinguished from $\mathrm{g}$, the symbol for a gram.^[ref]

A grain (unit) measures mass, whereas a minim measures volume. Converting a volume to a mass additionally requires the material's density, so these units cannot be substituted for one another. The exact conversion is useful when interpreting an older measurement without treating the mass of an individual seed as a physical standard.

A grain is a unit of mass that is traditionally used in the field of measurement for small weights. It is defined as exactly 64.79891 milligrams, which is equivalent to approximately 0.065 grams. The grain has been historically used for measuring precious metals, gemstones, and in various fields including pharmacology.