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Pediatric Medication Dosage Calculator

Calculates the volume of liquid medication to give a child based on weight, recommended dose, and drug concentration. Use it when preparing common pediatric medicines like acetaminophen or amoxicillin at home or in a clinical setting.

Last updated: September 2026

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Not medical advice. This calculator gives an estimate for general information only. It is not medical advice and does not replace a doctor, pharmacist or other qualified health professional. Always check with them before acting on the result, especially for medication doses, children, pregnancy or a medical condition, and follow the guidelines of your local health authority.

Formula below · 3 sources (medlineplus.gov, healthychildren.org, aap.org) · Updated Sep 2026

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About this calculator

Weight-based dosing is the standard approach in pediatrics because a child's ability to metabolize drugs scales closely with body mass. This calculator works with the dose per single administration (mg/kg per dose) and returns the volume for one dose. That distinction is critical: some drug labels state a dose per dose (e.g. ibuprofen 10 mg/kg per dose, acetaminophen 10–15 mg/kg per dose), while others state a total daily amount to be divided (e.g. amoxicillin 25–45 mg/kg per day divided into 2–3 doses). If your label gives a mg/kg/day figure, divide it by the number of daily doses yourself and enter that per-dose number here — entering a full daily amount would compute a single dose several times too large. Multiplying the per-dose mg/kg by the child's weight gives the milligrams for one dose: dose (mg) = childWeight (kg) × dosagePerKg (mg/kg/dose). Liquid pediatric formulations are labeled by concentration, commonly mg per 5 mL. Dividing the required milligrams by the concentration gives the number of 5-mL units; multiplying by 5 converts that to millilitres: volume (mL) = dose (mg) ÷ concentration (mg per 5 mL) × 5. The full formula is: volume = round[(childWeight × dosagePerKg / concentration) × 5 × 100] / 100. Always cross-check the calculated dose against the maximum single dose listed in the drug's package insert.

How to use

Example: a 20-kg child needs ibuprofen at 10 mg/kg, and the suspension has a concentration of 100 mg/5 mL. Enter Weight = 20, Recommended Dosage = 10, and Medication Concentration = 100 (the mg-per-5-mL figure printed on the bottle). Step 1 — Total dose: 20 kg × 10 mg/kg = 200 mg. Step 2 — Convert concentration to mg/mL: 100 mg / 5 mL = 20 mg/mL. Step 3 — Volume needed: 200 mg / 20 mg/mL = 10 mL. Round to two decimal places: 10.00 mL. Give 10 mL of the ibuprofen suspension per dose. Always use a calibrated oral syringe, not a household spoon.

Frequently asked questions

How do I calculate the correct acetaminophen dose for my child by weight?

The standard pediatric acetaminophen dose is 10–15 mg per kg of body weight, given every 4–6 hours as needed, with a maximum of 5 doses in 24 hours. For a 15-kg child at 15 mg/kg, the total dose is 225 mg. If the children's suspension is 160 mg per 5 mL (32 mg/mL), you would give 225 / 32 ≈ 7 mL. Never exceed the package's stated maximum dose for age and weight, and avoid using adult formulations in children.

Why is weight-based dosing important for children instead of a fixed dose?

Children are not simply small adults — their organ systems, especially the liver and kidneys responsible for drug metabolism and elimination, develop progressively. A fixed dose sized for an average child could be toxic for a small infant or completely ineffective for a large adolescent. Weight-based dosing anchors the prescription to the individual child's physiology, producing a therapeutic drug concentration with an acceptable safety margin. This is why pediatric drug labels always include a mg/kg guideline alongside the absolute maximum dose.

What does medication concentration in mg per 5 mL mean and why does it matter?

The concentration label tells you how many milligrams of active drug are dissolved in every 5 mL of liquid. This matters enormously because the same drug can come in multiple strengths — for example, amoxicillin suspension is available as 125 mg/5 mL, 200 mg/5 mL, and 400 mg/5 mL. Giving a dose calculated for one concentration using a bottle of a different concentration could mean delivering half or double the intended amount. Always read the concentration on the specific bottle you have in hand before measuring.

Should I enter the per-dose or the per-day dosage?

Enter the dose per single administration (mg/kg per dose) — this calculator returns the volume for one dose, not a daily total. Drug labels are not consistent about which they quote: ibuprofen (typically 10 mg/kg per dose) and acetaminophen (10–15 mg/kg per dose) are written per dose, whereas many antibiotics such as amoxicillin are written as a total per day (e.g. 25–45 mg/kg/day) that must be split across 2–3 doses. If your label gives a per-day figure, divide it by the number of doses per day first and enter that per-dose result. Entering a full daily mg/kg figure here would calculate a single dose that is two to three times too large. When in doubt, confirm the intended per-dose amount with your pharmacist or prescriber before giving the medication.

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