Pediatric Dose Calculation by Weight (mg/kg): A Practical Guide
Short answer: To calculate a pediatric dose by weight, multiply the child's weight in kg by the dose in mg/kg to get mg per dose, then divide by the syrup strength in mg per ml to get ml per dose. For example, paracetamol at 15 mg/kg for a 12 kg child is 180 mg; with a 250 mg/5 ml syrup (50 mg/ml) that is 3.6 ml per dose. Always check the result against the maximum single and daily adult dose, use today's measured weight, and confirm the product's strength because syrups and drops differ.
Weight-based dosing is simple arithmetic done hundreds of times a week, often by a tired doctor in a crowded OPD, with syrups that come in three strengths. That combination is why dosing errors in children are common. This guide covers the method and the traps; always verify doses against a current formulary.
In this guide
- The three-step formula
- Worked examples
- Common errors and how to avoid them
- Frequently asked questions
The three-step formula
Worked examples
| Drug (typical dose) | Child | Calculation | Result |
|---|---|---|---|
| Paracetamol 15 mg/kg every 4–6 h | 12 kg | 12 × 15 = 180 mg; syrup 250 mg/5 ml (50 mg/ml): 180 ÷ 50 | 3.6 ml |
| Paracetamol 15 mg/kg | 12 kg | 180 mg; syrup 120 mg/5 ml (24 mg/ml): 180 ÷ 24 | 7.5 ml |
| Ibuprofen 10 mg/kg every 6–8 h | 15 kg | 15 × 10 = 150 mg; suspension 100 mg/5 ml (20 mg/ml): 150 ÷ 20 | 7.5 ml |
| Amoxicillin 40 mg/kg/day in 2 doses | 10 kg | 400 mg/day → 200 mg/dose; 250 mg/5 ml (50 mg/ml) | 4 ml twice daily |
The two paracetamol rows show the most common error in practice: the same mg dose is 3.6 ml or 7.5 ml depending on which bottle the parent buys.
Common errors and how to avoid them
- Stale weight. Using last month's weight in an infant can be off by 10%. Weigh at every visit.
- Per-day vs per-dose confusion. Write "mg/kg/day divided into 3 doses" or "mg/kg/dose", never just "mg/kg".
- Drops vs syrup. Paracetamol drops (commonly 100 mg/ml) are many times stronger than syrup.
- Exceeding adult doses. A 45 kg adolescent at 15 mg/kg would get 675 mg; cap at the adult single dose.
- Decimal errors. Write 0.5 ml, never .5 ml; never write 5.0 ml.
- Kitchen spoons. Tell parents to use the measuring cup or an oral syringe in ml.
PediaNex calculates syrup volume from today's weight and your saved templates, then sends the prescription on WhatsApp.
Book a walkthroughFrequently asked questions
How do you calculate a pediatric dose by weight?
Multiply the child's weight in kg by the dose in mg/kg to get mg per dose, then divide by the medicine's concentration in mg/ml to get the volume in ml. Check the result does not exceed the adult maximum.
How much paracetamol syrup for a 10 kg child?
At a commonly used 15 mg/kg, a 10 kg child needs 150 mg per dose: 3 ml of 250 mg/5 ml syrup or 6.25 ml of 120 mg/5 ml syrup. Confirm with a formulary and the product label.
What is the difference between mg/kg/dose and mg/kg/day?
mg/kg/dose is the amount given at each administration; mg/kg/day is the total over 24 hours, which is then divided by the number of doses per day.
Should pediatric doses exceed adult doses for heavy children?
No. Weight-based doses should be capped at the standard adult dose for older or heavier children.
See weight-based prescriptions calculated and sent in seconds.
Twenty minutes, real workflow, no script. Or start the 15-day free trial.
Book a walkthrough or chat with us on WhatsApp →