Convert Grain to Milligram (gr → mg)

Converting grains to milligrams is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in grains

   Start with the number of grains (gr) you want to convert.
2. 2
   Multiply by 64.79891

   The conversion factor from gr to mg is 64.79891. Multiply your value by this number.
3. 3
   Read the result in milligrams

   The result is your value in milligrams (mg).

Multiply the value in grains by 64.79891. For the reverse direction, multiply by 0.015432.

• ✓1 grain = 64.79891 mg exactly. 7000 grains = 1 pound.
• ✓Ballistics is one of the few modern contexts where grains are essential.
• ✓Some older pharmacology dosing survives in grain units — 5 gr ≈ 325 mg.

• ✗Confusing the grain (mass) with the troy grain in older precious-metal contexts — they are identical (64.8 mg).
• ✗Assuming "grain" refers to an amount of cereal — in firearms it is always a weight.
• ✗Reading "5 gr" as 5 grams — it is 5 grains (324 mg).

What is the Grain?

The grain equals exactly 64.79891 milligrams (0.06479891 g) and is the smallest unit in the traditional avoirdupois weight system. Originally based on the average mass of a single grain of wheat or barley, the unit was standardized to its current value with the 1959 international yard and pound agreement. The grain is still used in pharmaceutical compounding (some older drug formulations specify grains, especially aspirin and codeine), arrow tips and ammunition (bullet weights are commonly given in grains — a 9 mm bullet is around 115 grains), and precious-metal weighing (one troy ounce = 480 grains). It relates to the ounce (437.5 grains = 1 oz avoirdupois), the pound (7,000 grains = 1 lb), and the milligram (1 grain ≈ 64.8 mg). The unit reflects medieval agriculture's role in shaping early measurement systems.

• Bullet and gunpowder mass in ballistics
• Older pharmaceutical dosing in Anglo-Saxon countries
• Arrow shaft and archery equipment weights

What is the Milligram?

The milligram equals one thousandth of a gram (0.001 g) or 10⁻⁶ kilograms, and is the standard unit for pharmaceutical dosing, vitamin labeling, food additives, and chemistry laboratory work. A typical aspirin tablet contains 325–500 mg of active ingredient, and recommended daily vitamin C intake is around 75–90 mg. The milligram is essential in toxicology (LD50 values are often given in mg per kg of body weight), water-quality testing (dissolved minerals in mg/L), and trace-element analysis. It relates to the gram (1,000 mg = 1 g), the microgram (1,000 µg = 1 mg), and the grain (1 grain ≈ 64.8 mg). Pharmaceutical prescriptions worldwide rely on milligrams, and accurate sub-milligram balances are standard in research and pharmacy environments.

• Prescription and over-the-counter drug dosing
• Vitamin and mineral supplement labelling
• Trace element analysis in laboratories