Medication Dosage by Weight Calculator
Calculate medication dosage in mg from body weight using mg/kg guidelines for adults and children.
Supports standard dose ranges and maximum daily dose limits.
Weight-based dosage calculation is the standard method used in pediatric medicine and for medications where therapeutic effect is tightly linked to body mass. The general formula is:
Dose (mg) = Weight (kg) × Dose Rate (mg/kg)
For liquid medications, a second step converts the dose to volume:
Volume (mL) = Dose (mg) / Concentration (mg/mL)
For divided daily doses:
Dose Per Administration = Total Daily Dose / Number of Doses Per Day
Worked Example — Ibuprofen for a child:
- Child weight: 22 kg (48 lbs)
- Dose rate: 10 mg/kg per dose
- Calculated dose: 22 × 10 = 220 mg
- Children’s ibuprofen concentration: 100 mg/5 mL
- Volume to give: 220 / (100/5) = 220 / 20 = 11 mL
- Maximum daily doses: 4× → total daily dose = 880 mg
Safety Boundaries:
- Ibuprofen: max 40 mg/kg/day, never exceed 2,400 mg/day for adults
- Acetaminophen: max 75 mg/kg/day, never exceed 4,000 mg/day
- Amoxicillin: typical 25–50 mg/kg/day in divided doses
IMPORTANT: This calculator is for educational reference only. Always follow a licensed prescriber’s instructions. Dosage can vary by kidney function, liver health, drug interactions, and the specific condition being treated. Never self-medicate based on a calculator result alone. Round calculated volumes to the nearest 0.5 mL to match syringe markings.