The least weighable quantity is defined as the amount that can be weighed accurately within a certain permissible % error (usually 5%). smallest quantity (mg): (100%) (balance sensitivity in mg) balance sensitivity in mg acceptable error as decimal acceptable error (%) 1. What is the smallest quantity that can be weighed with a potential error not more than 5% on a balance sensitive to 6 milligrams? Drug Dosage Based on Body Surface Area (BSA) height (cm) x weight (kg) BSA (m) = 3600 2. If the dose of a drug is 5 mg/m, what would be the dose for a patient with a BSA of 1.9 m?