Grain (gr)

US & ImperialTraditional unit (still used in some regions)

Exactly 64.79891 mg, based on the weight of a grain of barley. Still used for the weight of bullets, arrows and some medicines.

1 grain = 0.00006479891 kilograms (exactly).

About the grain

Barley and wheat seeds served as the earliest common weights in the Mediterranean, because a dry seed is small and fairly consistent. Medieval English law tied weights to the average mass of such grains, and the name grain stuck even after the link to actual cereal faded. The unit is exactly 64.79891 milligrams, fixed by the 1959 international yard and pound agreement, and NIST lists the same figure of 6.479891 x 10^-5 kilogram as exact.

Grain is unusual in being identical in the troy, avoirdupois and apothecaries' systems. A troy pound has 5,760 grains and an avoirdupois pound has 7,000. Modern use is mostly in niches: bullet and propellant weights, arrow weights in archery, and water hardness expressed as grains per gallon. Older drug doses were also given this way, with a standard 325 milligram aspirin tablet equal to five grains. Jewelers once used a pearl grain, a quarter of a carat. In the United Kingdom the unit has no legal standing for trade.

Sources: Wikipedia: Grain (unit); NIST SP 811 Appendix B.8 (conversion factors)

Grain conversion chart

1 grain expressed in every other weight & mass unit:

More US & Imperial units

• pound (weight & mass)
• ounce (weight & mass)
• dram (weight & mass)
• inch (length)
• foot (length)
• yard (length)
• mile (length)
• thou (length)
• league (length)
• furlong (length)
• chain (length)
• rod (length)
• link (length)
• hand (length)
• cubic inch (volume)
• cubic foot (volume)

All US & Imperial units

Browse all weight & mass units.