A box of .38 Special
cartridges that have 148-grain bullets
The grain is commonly used to measure the mass of bullets and propellants. The term also refers to a single particle of gunpowder, the size of which varies according to requirements. In archery, the grain is the standard unit used to weigh arrows.
In dentistry, gold foil, used as a material to restore teeth, is measured in grains.
In North America, the hardness of water is often measured in grains per US gallon (gpg) of calcium carbonate equivalents. Otherwise, water hardness is measured in the metric unit parts per million (ppm), equivalent to mg/L. One grain per US gallon is approximately . 17.1 ppm[note] Soft water contains 1–4 gpg of calcium carbonate equivalents, while hard water contains 11–20 gpg.
The 5-grain aspirin. The usage guidance label on a bottle of aspirin indicates that the dosage is "325 mg (5 gr)".
Though no longer recommended, grains are still used occasionally in medicine as part of the apothecaries' system, especially in prescriptions for older medicines such as aspirin or phenobarbital. For example, the dosage of a standard tablet of aspirin is sometimes given as 325 mg. 5 grains In that example the grain is approximated to , though the grain can also be approximated to 65 mg, depending on the medication and manufacturer. 60 mg The apothecaries system has its own system of notation, in which the unit's symbol or abbreviation is followed by the quantity in lower case Roman numerals. For amounts less than one, the quantity is written as a fraction, or for one half, ss (or variations such as ss., ṡṡ, or s̅s̅).:263 Therefore, a prescription for tablets containing 325 mg of aspirin and 30 mg of codeine can be written "ASA gr. v c̄ cod. gr. ss tablets" (using the medical abbreviations ASA for aspirin,:34:8 c̄ for "with",:56:14 and cod. for codeine).:70:19 The apothecaries' system has gradually been replaced by the metric system, and the use of the grain in prescriptions is now rare.
Particulate emission levels, used to monitor and regulate pollution, are commonly measured in grains per . This is the same unit commonly used to measure the amount of moisture in the air, also known as the absolute humidity. The SI unit used to measure particulate emissions and absolute humidity is mg/m3. One grain per cubic foot is approximately 3. 2288 mg/m[note]