What Is a Grain?
The grain (symbol gr) is one of the oldest units of mass, historically based on the weight of a single seed of grain such as barley or wheat. Today it is precisely defined: 1 grain = 0.06479891 grams (exactly 64.79891 milligrams). It is still widely used for measuring bullets, gunpowder and arrow points, the weight of precious metals and gemstones, and in pharmacy and aspirin dosing.
How to Use This Calculator
Enter the value you want to convert, choose the direction (grains → grams or grams → grains), and the result updates instantly. The tool uses the exact international conversion factor so results are accurate to many decimal places.
The Formula Explained
Converting grains to grams is a simple multiplication: $$\text{grams} = \text{grains} \times 0.06479891$$ To go the other way, divide instead: $$\text{grains} = \text{grams} \div 0.06479891$$ Because the factor is exact (defined by the international yard and pound agreement of 1959), no rounding is introduced beyond what your display precision allows.
Worked Example
Suppose you have a 150-grain bullet. Multiply: $$150 \times 0.06479891 = 9.7198365 \text{ grams}$$ Reversing it, \(9.7198365 \text{ g} \div 0.06479891 = 150\) grains, confirming the conversion.
FAQ
How many grains are in a gram? One gram equals about 15.4324 grains (\(1 \div 0.06479891\)).
Is a grain the same as a carat? No. A metric carat is 0.2 grams (about 3.086 grains), used for gemstones, while a grain is 0.0648 grams.
How many grains are in an ounce? An avoirdupois ounce contains exactly 437.5 grains.
