Calculating drug dosages and solutions for nursing school may seem like a daunting task, mostly because many nursing students report a discomfort with math. But learning how to calculate drug dosages is a moderately easy process if you learn a few simple formulas and practice working with math. There are three basic methods to calculate drug dosages and a simple formula to use to calculate intravenous flow rate. Resources are available in print and online to help nursing students practice calculating drug dosages. (See References.)
Calculate drug dosages and solutions

Use the basic formula method of calculating drug dosages. Divide dose ordered by the dose listed on the container label (or the dose on hand). Multiply the result by the form and amount of the drug to get the amount to give.

Use the ratio and proportion method of calculating doses  the formula H:V::D:X is the easiest way to remember this method. The lefthand ratio represents known quantities (dose listed on the container label or dose on hand, and the form and amount of the drug) while the righthand ratio represents one known quantity (dose ordered) and one unknown quantity (amount to give). Multiply dose ordered (D) times form and amount (V) and divide the result by the dose on the container (H). The result is the amount to give.

Use the fractional equation method of calculating drug doses. Multiply dose ordered by the form and amount of the drug; divide this result by the dose listed on the container label. The result is the amount to give.

Calculate intravenous flow rate by multiplying the amount of fluid by the drops per milliliter in the IV set and then divide that result by the number of hours to administer multiplied by the number of minutes per hour (60).
Tips & Warnings
 Remember when working with formulas to convert units of measurement into consistent measurements, e.g., all numbers in milligrams or milliliters instead of trying to work with milligrams and deciliters.
References
 Dosage Calculations Made Incredibly Easy!, 4th Edition.
 Drug Calculation Practice for Nurses