Grain (gr)
The grain is one of the oldest and smallest traditional units of mass, equal to exactly 64.79891 milligrams. It is the only unit of mass shared by the avoirdupois, troy, and apothecaries' systems. Today the grain survives primarily in two fields: ammunition (bullet weights) and pharmacy (though milligrams have largely replaced it in modern prescriptions).
Definition
One grain equals exactly 64.79891 milligrams, 0.06479891 grams, 1/7,000 of an avoirdupois pound, 1/480 of a troy ounce, or 1/20 of a scruple. There are 437.5 grains in an avoirdupois ounce and 480 grains in a troy ounce. The grain is identical across the avoirdupois, troy, and apothecaries' weight systems.
History
The grain is believed to originate from the weight of a single grain of wheat or barleycorn. Ancient civilizations, including the Mesopotamians, Egyptians, and Greeks, used cereal grains as primitive weight standards because they were reasonably uniform and universally available. The English grain was standardised as 1/7,000 of an avoirdupois pound, 1/5,760 of a troy pound, and 1/5,760 of an apothecaries' pound - making it the unique unit common to all three systems. In 1959, the grain was fixed at exactly 64.79891 milligrams through the International Yard and Pound Agreement.
Common Uses
In firearms and ammunition, bullet weights and gunpowder charges are universally specified in grains. A 9mm bullet typically weighs 115-147 grains, and an arrow for archery is specified in grains per inch. In pharmacy, aspirin was historically dosed at 5 grains (about 325 mg) per tablet, and some older pharmaceutical references still use grains. Gold leaf thickness is sometimes given in grains per sheet. Reloading (handloading) ammunition requires precise grain measurements for both projectiles and propellant charges.
Did You Know? Facts About Grain
- A standard aspirin tablet of 325 mg is exactly 5 grains - the dosage was originally defined in grains, not milligrams.
- The grain is the only unit of weight that is identical in the avoirdupois, troy, and apothecaries' systems.
- A typical 9mm bullet weighs about 124 grains (8.0 grams).
- The grain was supposedly based on the weight of a barleycorn, but actual barleycorns vary from about 40 to 70 mg.
- Despite its ancient origins, the grain is actively used every day by millions of competitive shooters and reloaders worldwide.