TheUnited States Pharmacopeiagives specifications for fill weight variation of capsules, tablets, and sterile solids to which the federal government expects the pharmaceutical industry to adhere. This paper makes probability statements about the USP weight variation test that could form the basis for a criterion for both final product release and in-process control, as far as fill weight variation is concerned. Use is made of the fact that the coefficient of variation, the standard deviation divided by the mean, efficiently describes fill weight variation. The effect of un-intentional overfill on control is considered. A certain final product weight variation specification is examined and mention is made of sampling methods.