Pediatric Dose Calculator
Work out a child’s weight-based medication dose. Enter the prescribed dose, the dosing basis (per dose or per day), how often it is given, and the product strength to get the milligrams per dose, the daily total, and the exact liquid volume in millilitres to measure out. An optional maximum cap keeps a single dose under the safe ceiling.
Formula
Worked example
A 20 kg child on 15 mg/kg per dose: 20 × 15 = 300 mg per dose. With acetaminophen at 160 mg per 5 mL, the volume is 300 ÷ 160 × 5 = 9.4 mL per dose. Given four times a day, the daily total is 1200 mg.
How weight-based pediatric dosing works
Children are not small adults, so most pediatric medicines are dosed by body weight rather than by a fixed amount. The prescriber or label gives a number of milligrams of drug per kilogram of body weight, either per single dose (mg/kg/dose) or per day (mg/kg/day). For a per-dose figure you multiply it by the child’s weight in kilograms. For a per-day figure you multiply by weight and then divide by the number of doses given each day to get the size of one dose. A heavier child receives proportionally more, which keeps blood levels in the effective range across a wide span of ages and sizes. Always use a recent, accurately measured weight, since an over- or under-estimate feeds straight into the result.
From milligrams to millilitres
A dose in milligrams only tells you how much drug to give, not how much liquid to pour. To find the volume you need the product strength, written on the bottle as a mass per volume, for example 160 mg per 5 mL. The volume per dose is the dose in milligrams divided by that strength and multiplied by the stated volume. The same arithmetic works for tablets if you enter the tablet strength per one unit. Concentrations differ widely between brands and between infant and child formulations, so always read the specific label and measure with a marked oral syringe rather than a household spoon, which can be off by a factor of two.
Frequency, daily totals and the maximum dose
How often a drug is given matters as much as the size of one dose. The frequency setting both splits a per-day amount into individual doses and multiplies a per-dose amount up to a daily total, so you can check the order against any maximum daily limit. Weight-based scaling also has a ceiling: once a child approaches adult size the weight-based figure would exceed the largest dose ever given to an adult, which adds risk without benefit. The optional maximum cap takes whichever is smaller, the weight-based dose or the maximum, so a single dose never goes over the safe ceiling. The per-dose cap is separate from the maximum daily dose, check both.
Costing a course and good practice
Turn on the cost estimate to price a full course of a liquid medicine. The calculator multiplies the volume per dose by the doses per day and the number of days to find the total liquid needed, then rounds up to whole bottles of the size you buy and applies the price. The figure is a planning estimate, prices and bottle sizes vary by pharmacy and country. Whatever the numbers, this tool is an arithmetic aid, not medical advice: it does not account for the child’s age, kidney or liver function, other medicines or allergies. Clinical decisions about which drug, dose, frequency and route to use must be made by a qualified prescriber or pharmacist. If a result looks unexpected, stop and confirm before giving anything.
Common liquid strengths (mass per volume)
| Medicine (example) | Stated strength | mg per mL |
|---|---|---|
| Acetaminophen (children) | 160 mg / 5 mL | 32 mg/mL |
| Acetaminophen (infant) | 160 mg / 5 mL | 32 mg/mL |
| Ibuprofen (children) | 100 mg / 5 mL | 20 mg/mL |
| Ibuprofen (infant) | 50 mg / 1.25 mL | 40 mg/mL |
| Amoxicillin | 250 mg / 5 mL | 50 mg/mL |
Illustrative only. Always read the strength printed on the specific bottle, since brands and infant versus child formulations differ.
Frequently asked questions
Is the result a single dose or a daily total?
The primary result is one single dose, the amount for a single administration. The calculator also shows the daily total, which is the single dose multiplied by the number of doses per day. Many drugs have a separate maximum daily dose, so always follow the frequency the prescriber ordered and do not exceed any daily limit on the label.
How does it convert milligrams to millilitres?
It uses the product strength you enter, written as a mass per volume such as 160 mg per 5 mL. The volume per dose is the dose in milligrams divided by that mass and multiplied by the volume. For a 300 mg dose at 160 mg per 5 mL that is 300 ÷ 160 × 5, about 9.4 mL. Enter the tablet strength per one unit to work in tablets instead.
What is the difference between mg/kg/dose and mg/kg/day?
A mg/kg/dose figure is the amount for one single dose, so you multiply it by weight and give that amount each time. A mg/kg/day figure is the total for a whole day, so after multiplying by weight you divide by the number of doses per day to size one dose. Picking the wrong basis can multiply or divide the dose by the frequency, so match the label exactly.
Should I use weight in kilograms or pounds?
Dose-per-kg figures are defined in kilograms. If you enter pounds, the calculator converts to kilograms first (1 lb is about 0.4536 kg) before multiplying. Using pounds directly with a mg/kg figure would roughly double the dose, so always convert.