A 20 kg child, amoxicillin 25 mg/kg/day, three times daily, 250 mg/5 mL suspension
Total daily dose is 500 mg, 166.7 mg per dose, given as 3.33 mL of a 50 mg/mL suspension.
Pediatric weight-based dosage calculator
For healthcare professional reference only. This performs arithmetic on the values entered — it does not verify that the prescribed dose is clinically appropriate, and it is not a substitute for checking the prescription, the drug’s dosing limits, and a pharmacist’s independent double-check. Never give a medication dose based solely on this page.
Result
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How it works
Weight-based dosing scales the total amount of drug to the size of the patient, which matters far more in children than adults because body weight varies enormously across paediatric ages — a fixed adult dose would badly overdose an infant or underdose a teenager.
The prescribed rate is a total for the day, which then needs dividing by however many separate administrations the dosing schedule calls for (twice, three or four times daily are common), and finally converting from a mass (mg) to a volume (mL) using the specific formulation’s concentration, since two products with the same drug can be sold at very different strengths.
Formulas used
Total daily dose
Total daily dose (mg) = weight(kg) × prescribed dose(mg/kg/day)
Dose per administration and volume
Dose per administration = total daily dose / doses per day; Volume = dose per administration / concentration
Worked examples
A 12 kg infant, 15 mg/kg/day, twice daily, 125 mg/5 mL suspension
Total daily dose is 180 mg, 90 mg per dose, given as 3.6 mL of a 25 mg/mL suspension.
Assumptions and limits
- The mg/kg/day figure is assumed already clinically appropriate for the specific drug, indication and patient — this only performs the arithmetic.
- No maximum single-dose or maximum daily-dose cap is applied; some drugs have an absolute ceiling regardless of weight, which is not checked here.
Frequently asked questions
Where does the mg/kg/day figure come from?
From the prescriber’s order or the drug’s approved paediatric dosing reference — it is a clinical decision based on the specific drug, the condition being treated and the child’s age, never something to look up generically and apply to any medication.
What if the calculated volume doesn’t match a convenient measuring mark?
Round to what the dosing device (oral syringe, dosing cup) can actually measure precisely, and check with a pharmacist if the difference from the calculated ideal is more than a small rounding adjustment — administering an imprecisely measured dose is a common source of paediatric dosing error.
Updated