Dosage by Weight Calculator

Weight, kg

Dose, mg per kg

Doses a day

Concentration, mg

The active amount in the volume below.

Per how many ml

Daily cap, mg per kg

Result

Single dose, mg300
That is ml of syrup12.5
Daily dose, mg900
Daily dose, mg/kg45
Interval between dosesevery 8 h
Cap checkWithin the limit: 45 mg/kg a day of 60

This result is informational only and is not professional advice.

Milligrams, millilitres and the ceiling

Works out a single and daily dose from body weight, converts it into millilitres of a liquid formulation, and checks it against a daily cap.

Paediatric doses are written in milligrams per kilogram while the measuring spoon is marked in millilitres. Between the two sits the concentration of the syrup — 120 milligrams in five millilitres, say — and that conversion is where most mistakes happen.

The second common error is forgetting the daily ceiling. A single dose can be right and still put the daily total over the limit once it is given four times instead of three. This calculator works out both and compares the daily figure with the cap you enter.

What this calculator shows

The single dose in milligrams and in millilitres of the prepared form
The daily dose in milligrams and in milligrams per kilogram
A check against the daily cap and the interval between doses

What to keep in mind

The calculator knows nothing about any particular medicine: the dose per kilogram, the concentration and the cap all come from the label or the prescription.
This is arithmetic, not a prescription. Drug, dose and duration are a clinician's decision, and kidney or liver impairment changes them further.

FAQs

How do I convert milligrams to millilitres?

Divide the dose in milligrams by the concentration and multiply by the volume it is quoted in. For 300 mg at 120 mg per 5 ml, that is 12.5 ml.

What if a child falls between the listed doses?

Dose by actual weight rather than age: the age bands on a label are an average. Where there is doubt, a pharmacist or doctor should confirm.

Why does the daily cap matter?

Because overshoot accumulates. With paracetamol, for instance, it is the daily total rather than a single dose that drives the risk of liver injury.

Can I round the dose?

Rounding slightly down to a convenient syringe mark is usually acceptable; rounding up is not. The label is the authority for any specific medicine.

Worked example

Syrup for a 20 kg child

Input: 20 kg, 15 mg/kg, three times a day, 120 mg in 5 ml, cap 60 mg/kg

Output: 300 mg per dose — that is 12.5 ml, 900 mg a day

Note: The daily 45 mg/kg fits inside the 60 mg/kg cap. Four doses instead of three would land exactly on 60, and five would go over it.

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Result

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