Tips for Drug Calculations

  Always convert everything to the same units before solving the calculation.

  Complete work from left to right.

  Follow the one unit or by proportion rule: what you do to one side of an equation, do the same to the other side.

  Write out the calculation clearly.

  Write down every step. Do not take short cuts; you are more likely to make a mistake.

  If you are copying formulas from a reference source, double-check your work.

  Try not to depend on your calculator. Gestimate your answer, then if you make a mistake on the calculator, you are more likely to know that an error has been made.

  If you are in doubt about a calculation, stop and get help.

  When administering intravenous (IV) infusions, you need to know: the flow rate, infusion time, and total volume.


Use the following equations:

  flow rate (mL/hr) = total volume (mL) infusion time (hr)

  infusion time (hr) = total volume (mL) flow rate (mL/hr)

  total volume (mL) = flow rate (mL/hr) infusion time (hr)