Grams & Milligrams: 1 grain = 60 mg

First, if you are trying to convert grains to milligrams, simply multiply the number of grains by 60.

Second, if you are attempting to convert milligrams to grains, simply divide the number of milligrams by 60.

Example: Convert 5 gr to milligrams: 5 X 60 = 300 mg
Convert 180 mg to grains: 180 / 60 = 3 gr