Paediatric Dose (Clark Rule) Calculator

Work out paediatric dose (clark rule) instantly with clear inputs, formula shown and shareable results.

About Paediatric Dose (Clark Rule) Calculator

Applies Clark's rule, which scales an adult dose by the child's weight in pounds divided by a 150 pound adult reference.

Formula

Clark's rule

Child dose = adult dose x weight (lb) / 150

Worked example

With the default values below, Paediatric Dose (Clark Rule) Calculator returns Estimated child dose of 147.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Adult doseaccepts 1–5,000 mg: 500 mg
Child weightaccepts 1–80 kg: 20 kg

Results

Estimated child dose: 147.0 mg
Weight in pounds: 44.1 lb
Share of the adult dose: 29.4%

Step by step

1Values used
2Clark's rule
3Estimated child dose= 147.0 mg
4Weight in pounds= 44.1 lb
5Share of the adult dose= 29.4

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.
This is an estimate for general information and not professional medical advice. See the full disclaimer for the limits that apply to this kind of calculator.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Educational estimate only. Not a substitute for professional clinical judgement, and must not be used to make treatment or dosing decisions.

Frequently Asked Questions

Is Clark's rule still used?

Rarely in practice. Modern paediatric dosing uses mg/kg or mg/m2 values from a formulary; Clark's rule remains a teaching tool.

Why 150 pounds?

It represents a nominal 68 kg adult, the reference body size behind the adult dose.