Medication Dosage by Weight Calculator
Calculate the correct medication dosage based on body weight using mg/kg dosing.
Supports adults and children in metric and imperial units.
How Medication Dosage Calculations Work
Medication dosage calculations determine how much of a drug to administer based on prescribed dose, patient weight, and available concentration. These calculations are critical for patient safety — errors are a leading cause of preventable harm.
Basic dose calculation:
Volume to administer = Prescribed dose ÷ Available concentration
Worked example — liquid antibiotic:
- Prescribed: amoxicillin 375 mg
- Available: 250 mg/5 mL suspension
Volume = 375 ÷ (250/5) = 375 ÷ 50 = 7.5 mL
Weight-based dose calculation (most common in pediatrics and IV medications):
Total dose = Weight (kg) × Dose per kg
Volume = Total dose ÷ Concentration
Example — IV gentamicin:
- Patient weight: 68 kg
- Order: 5 mg/kg IV once daily
- Available: 40 mg/mL
Total dose = 68 × 5 = 340 mg Volume = 340 ÷ 40 = 8.5 mL
Drip rate calculation for IV infusions:
Drip rate (mL/hr) = Volume (mL) ÷ Time (hr)
If 500 mL must infuse over 4 hours:
Drip rate = 500 ÷ 4 = 125 mL/hr
Drop rate (manual drip sets):
Drops per minute = (Volume mL × Drop factor) ÷ (Time in minutes)
Standard drop factor: 10, 15, or 20 drops/mL depending on the IV set.
The Five Rights of medication administration:
Right patient · Right drug · Right dose · Right route · Right time
Always double-check by having a second clinician independently verify calculations for high-alert medications (insulin, heparin, chemotherapy). A tenfold dosing error is more common than most people realize.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.