Work out the daily dose, the single dose and the liquid volume from a child’s weight, the mg/kg dose and the number of doses, with the maximum applied.
kg
mg/kg/day
mg/mL
For example a 250 mg/5 mL suspension is 50 mg/mL.
mg
Enter the values to see the result here.
Check the dose against the approved drug reference and the liquid strength before giving it. This tool only does the arithmetic.
Formula
With weight W in kg, daily dose D in mg/kg/day and n doses per day:
If a maximum daily dose is entered, the daily dose is limited to it before dividing.
Worked example
A child weighs 15 kg. The drug is 40 mg/kg/day in 3 doses, as a 50 mg/mL liquid.
Daily dose: 15×40=600 mg.
Each dose: 600/3=200 mg.
Volume: 200/50=4 mL three times a day.
With a maximum of 500 mg/day the daily dose is limited to 500 mg and each dose is 166.7 mg.
Common mistakes
Confusing mg/kg/day with mg/kg per dose, which triples or quadruples the result.
Using a weight in pounds. Divide pounds by 2.2 to get kilograms.
Misreading the liquid strength, for example using 125 instead of 25 mg/mL.
Ignoring the maximum dose for heavy children, or dosing an obese child on total weight when the reference says ideal weight.
Frequently asked questions
Is the mg/kg figure per dose or per day?
It differs by drug and the reference states which. This tool takes the total daily dose in mg/kg/day and divides it by the number of doses. If your reference gives mg/kg per dose, multiply by the number of doses first, or enter the dose once and set doses per day to 1.
Why does the maximum daily dose matter?
Weight-based dosing scales linearly, so a heavy child can reach an adult overdose. Every paediatric reference lists a ceiling, usually the adult maximum, and the lower of the two should be given.
How do I read a suspension strength such as 125 mg/5 mL?
Divide the milligrams by the millilitres: 125 / 5 = 25 mg/mL. Enter 25 and the tool gives the volume in mL for each dose.