How many grains equal a milligram?

In the most common definition of the grain unit of measurement, there are 64.8 mg in 1 grain, so there are about 0.016 grains in 1 mg. This grain unit is also known as a troy grain, an avoirdupois grain and an apothecary's grain. The metric grain or jeweler's grain is used to indicate the weight of diamonds and pearls and 1 metric grain is ¼ carat or 50 mg.

The grain is conceptually defined as the weight of one grain of barley. Modern uses of the grain unit include the measurement of:

• Bullets
• Gunpowder
• Gold for dental use
• Hardness of water (in the U.S. only)
• Particulate emissions levels
• Humidity
• Medications