Pediatric Weight-Based Dose Calculator
Free pediatric weight-based dose calculator. Enter weight in kg and the mg/kg order to get the daily dose, per-dose amount and liquid volume instantly.
Updated 2026-06-14 · Free · No sign-up · Runs privately in your browser
Show the formula & steps
Educational tool only. Always confirm dosing against the prescription, the drug label and a pharmacist. Not medical advice.
How the Pediatric Weight-Based Dose Calculator Works
Many medicines for children are dosed by body weight rather than by age. This calculator does the standard arithmetic for you: enter the child’s weight in kilograms, the ordered dose in mg/kg/day, the number of doses per day, and optionally the liquid concentration in mg/mL. It returns the total daily dose, the amount per dose, and the volume to measure for each dose.
The Formula
Total daily dose (mg) = weight (kg) × dose (mg/kg/day) Per dose (mg) = total daily dose ÷ doses per day Volume per dose (mL) = per dose (mg) ÷ concentration (mg/mL)
If your prescription is written as mg/kg/dose rather than per day, simply set “doses per day” to 1, and the per-dose result will equal weight × the value you entered.
Worked Example
A medication is ordered at 40 mg/kg/day divided into 3 doses, for an 18 kg child, using a suspension that is 250 mg/5 mL (50 mg/mL):
- Total daily dose = 18 × 40 = 720 mg/day
- Per dose = 720 ÷ 3 = 240 mg per dose
- Volume per dose = 240 ÷ 50 = 4.8 mL per dose
Converting Pounds to Kilograms
Pediatric dosing nearly always uses kilograms. If you only know the weight in pounds, divide by 2.2046:
| Weight (lb) | Weight (kg) |
|---|---|
| 22 | ≈ 10.0 |
| 33 | ≈ 15.0 |
| 44 | ≈ 20.0 |
| 66 | ≈ 30.0 |
Important Safety Notes
This tool performs arithmetic only. It does not know the correct dose for any specific medication, the maximum safe dose, the appropriate frequency, or any drug-specific warnings. A correct calculation of the wrong order is still wrong. Always:
- Confirm the mg/kg order and the maximum dose against a trusted reference and the prescriber.
- Verify the concentration printed on the actual bottle, since the same drug comes in different strengths.
- Have a pharmacist or clinician double-check before administering.
This calculator is for education and is not medical advice.
Frequently asked questions
How do you calculate a weight-based pediatric dose?+
Multiply the child's weight in kilograms by the ordered dose in mg per kg. For a 20 kg child at 30 mg/kg/day, the total daily dose is 20 × 30 = 600 mg/day. Divide by the number of doses per day to get each individual dose.
How do I convert a dose in mg to a liquid volume in mL?+
Divide the dose in milligrams by the liquid's concentration in mg per mL. If a per-dose amount is 200 mg and the suspension is 250 mg per 5 mL (50 mg/mL), the volume is 200 ÷ 50 = 4 mL. Always check the concentration printed on the label.
Do I use total body weight in kilograms?+
Most pediatric dosing uses actual body weight in kilograms unless the order or reference specifies otherwise (for example, ideal or adjusted body weight for some drugs). To convert pounds to kilograms, divide by 2.2046. A 44 lb child weighs about 20 kg.
What is mg/kg/day versus mg/kg/dose?+
mg/kg/day is the total amount for the whole day, which you then divide by the number of doses. mg/kg/dose is the amount for each single dose. This calculator treats the ordered value as mg/kg/day and divides by the doses-per-day field; if your order is per dose, set doses per day to 1.
Is this calculator safe to use for real prescriptions?+
No. This is an educational arithmetic tool. It does not know the correct dose, maximum limits, or safety information for any specific drug or child. Always confirm the order, the maximum dose, and the concentration with the prescription, the drug label and a pharmacist before giving any medication.