A grain is just an old system of weight. 1 grain is about 64 mg. I was tested on grain based dosages in school but never saw them used in real life.
General rules:
Exceptions may be made at the discretion of the mods.
A grain is just an old system of weight. 1 grain is about 64 mg. I was tested on grain based dosages in school but never saw them used in real life.