Many medicines, especially for children, are prescribed per kilogram of body weight. Dosing errors – such as confusing mg and mL or misplacing a decimal point – are a common cause of harm, so every calculation should be double-checked against the label or by a pharmacist.
How to use the Dosage Calculator
- Weight
- Prescribed dose
- Doses per day
- Liquid concentration
- Maximum single dose (0 = none)
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the weight, the prescribed mg/kg dose, the number of doses per day and the liquid concentration. Enter a maximum single dose to cap the result if your prescriber gave one.
Inputs explained
| Field | What to enter |
|---|---|
| Weight | Units: kg, lb, st, g |
| Prescribed dose | In mg/kg per dose |
| Doses per day | A number |
| Liquid concentration | In mg/mL |
| Maximum single dose (0 = none) | In mg |
What each result means
- Volume per dose = [Dose per administration]÷[Liquid concentration]
- Total per day = [Dose per administration]×[Doses per day]
- Interval between doses = 24÷[Doses per day]
Example values
How the main result changes when Weight changes and everything else stays at the example values above:
| Weight (kg) | Dose per administration (mg) |
|---|---|
| 10 | 100 |
| 15 | 150 |
| 20 | 200 |
| 25 | 250 |
| 30 | 300 |
| 40 | 400 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
Dose per administration = weight (kg) × dose (mg/kg)
Volume (mL) = dose (mg) ÷ concentration (mg/mL)
Daily total = dose × doses per day (check against the maximum daily dose)
Worked example
Inputs — Weight: 20 kg; Prescribed dose: 10 mg/kg per dose; Doses per day: 3; Liquid concentration: 40 mg/mL; Maximum single dose (0 = none): 0 mg.
Results — Dose per administration = 200 mg; Volume per dose = 5 mL; Total per day = 600 mg; Interval between doses = 8 hours.
Key terms
- mg/kg
- Milligrams of medicine per kilogram of body weight.
Frequently asked questions
How do I measure a liquid dose accurately?
Use an oral syringe or the measuring device supplied – never a kitchen spoon.
What if the calculated dose exceeds the adult dose?
Never exceed the maximum stated on the label or by the prescriber.
Should I use actual or ideal weight?
Follow the medicine's guidance – some use ideal or adjusted weight in obesity.