The drug dosage calculator helps nurses calculate the exact volume of liquid medication to administer when the ordered dose and available concentration differ. It uses the standard nursing D/H × Q formula — Desired divided by Have, multiplied by Quantity — which is the foundation of safe medication administration in clinical practice. Use this tool as a quick double-check before drawing up any liquid medication.
Before administering any medication, confirm: Right Patient · Right Drug · Right Dose · Right Route · Right Time. Always double-check high-alert medications with a second nurse.
The standard nursing drug dosage formula is D/H × Q, where D is the desired (ordered) dose, H is the dose on hand (available), and Q is the quantity (volume) available. For example, if 250mg is ordered and the available concentration is 125mg/5mL, the volume to give is (250 ÷ 125) × 5 = 10 mL.
Always double-check drug dose calculations for high-alert medications (insulin, heparin, opioids, chemotherapy), paediatric doses, and any result greater than 10 mL for a single dose. Most institutions require an independent double-check by a second nurse for these drug categories.