Before calculations are performed, all units involved should be converted into one system, notes NursesAreGreat.com. There is a basic formula, which is frequently used to calculate drug dosages. Other methods used include ratio and proportion, fractional equation, intravenous flow rate calculation and continuous infusions.
The basic formula states that D/H * V = amount to give. In this formula, D refers to the ordered or desired dose, H refers to the dose on container label or on hand, and V refers to amount and form of drug, such as tablet, capsule or liquid, explains NursesAreGreat.com. The ratio and proportion method, H : V :: D : x, is the oldest method used for calculating doses, where H and V are known values, and D and x represent the desired dose and amount to give. D and V are multiplied to equal the product of H and x. The fractional equation states that H/V = D/x. For both of these methods, x must be solved for.