Medication Dosage Calculator — Dose per kg Body Weight
Convert a weight-based dose (per kg per day or per single dose) into single, daily and weekly amounts. For guidance only; it does not replace medical advice.
Not a substitute for medical advice
This calculator is for guidance only. Actual dosage must always be determined by a doctor or pharmacist. No self-medication without medical consultation!
Leaflets say e.g. "50 mg/kg/day in 3 divided doses" (= per day) or "15 mg/kg per dose". Choosing the wrong option multiplies or divides the result by the number of doses.
Note: These calculations are for informational purposes only and do not replace professional tax or financial advice. All information without guarantee.
FAQ
Frequently Asked Questions
Does the mg/kg figure apply per dose or per day?
The package leaflet or prescribing information (Fachinformation) says which, and you need to check it before calculating. "15 mg/kg as a single dose" refers to each individual dose; "50 mg/kg/day in 3 divided doses" is the amount for the whole day. Choose "per single dose" or "per day" in the calculator accordingly. Mixing them up is dangerous: if a daily figure is calculated as a single dose, the result is three times the intended amount with 3 doses a day.
Why are doses for children calculated by body weight?
Children need very different amounts of an active ingredient depending on their size, so many package leaflets for children give a dose per kg of body weight or weight bands. The current weight is what counts. The maximum single and daily dose from the package leaflet or prescribing information must not be exceeded even if the calculation gives more – for heavier children and adolescents, the adult dose is usually the upper limit. Infants, premature babies and patients with kidney or liver disease often follow different rules; the doctor decides.
How does the calculator work out the single and daily dose?
For a figure per day: daily dose = body weight × dose per kg, single dose = daily dose ÷ doses per day. For a figure per single dose: single dose = body weight × dose per kg, daily dose = single dose × doses per day. The weekly amount is always daily dose × 7. Example: 20 kg and 50 mg/kg per day in 3 doses gives 1,000 mg per day and about 333.3 mg per dose; 20 kg and 15 mg/kg per single dose with 4 doses gives 300 mg per dose and 1,200 mg per day. The calculator does not check maximum amounts, age or kidney and liver function, and it does not convert mg into drops, millilitres of syrup or tablets – that would require the concentration of the active ingredient. The result usually has to be rounded to an available tablet strength or a measurable volume; your doctor or pharmacist decides how.
Guide
What is the Medication Dosage Calculator — Dose per kg Body Weight?
The medication calculator converts a weight-based dosage (e.g. mg per kg of body weight) into the amount per dose, per day and per week. It does not replace the package leaflet or advice from a doctor or pharmacist.
How does the Medication Dosage Calculator — Dose per kg Body Weight work?
Enter the body weight and the dose per kg from the prescription, package leaflet or prescribing information (Fachinformation), choose the unit (mg, mcg or ml per kg) and set whether the figure applies per day or per single dose. Together with the number of doses per day: for a daily figure, the daily dose (weight × dose) is split across the doses; for a per-dose figure, the single dose (weight × dose) is multiplied by the number of doses.
Key Data and Facts
Dosage figures apply either per single dose (e.g. 15 mg/kg per dose) or per day (e.g. 50 mg/kg/day in 3 divided doses) – many package leaflets, for example for children's antibiotic suspensions, give mg/kg per day. Mixing them up makes the dose too high or too low by a factor of the number of doses. Never exceed the maximum single and daily dose stated in the package leaflet or prescribing information; the calculator does not check maximum doses. Always follow your doctor's or pharmacist's instructions.
Calculation Example
Child weighing 20 kg, 50 mg/kg per day in 3 doses: daily dose 20 × 50 = 1,000 mg, single dose 1,000 ÷ 3 ≈ 333.3 mg. 15 mg/kg per single dose, 4 times a day: single dose 20 × 15 = 300 mg, daily dose 4 × 300 = 1,200 mg. With a suspension containing 250 mg per 5 ml, 333.3 mg works out at about 6.7 ml – the measurable amount to round to is decided by the doctor or pharmacist.
Sources
Official sources
Calculations are based on applicable German laws and official data:
Full methodology at Methodology.
Reviewed by Konstantin Iakovlev · Last updated:
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