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Pediatric Dose Calculator

Find a pediatric dose by weight.

How it is calculated

The tool applies Clark's rule in its metric form: child dose = adult dose × weight / 70. The adult dose is in whatever unit you enter (for example mg), the child's weight is in kilograms, and 70 kg is the reference adult weight. The result has the same unit as the adult dose and is rounded to two decimals.

Only the weight is used; age, kidney or liver function and the drug's own limits are not considered. A weight below zero gives no answer. Many medicines have their own paediatric dosing tables, which always take priority over this proportional rule. This is an educational calculation and not medical advice.

Worked example

Adult dose 500 mg, child weight 21 kg. Weight ratio = 21 / 70 = 0.3. Child dose = 500 × 0.3 = 150. The tool shows 150.00, which is 150 mg in the unit you entered.

Try this example →

Common mistakes

  • Entering the child's weight in pounds; the 70 in the formula is kilograms, so the dose would come out more than twice too high.
  • Entering the child's usual dose in the adult field instead of the standard adult dose.
  • Using the result for a drug that has its own mg/kg or age-band schedule, which can differ a lot from simple scaling.
  • Forgetting that the result is in the same unit as the dose you typed (mg vs mL of a liquid with a given concentration).

About this calculator

This calculator applies Clark's rule, one of the classic weight-based dosing formulas: child dose = (child's weight in pounds ÷ 150) × the standard adult dose. It scales an adult medication amount down to a size appropriate for a much smaller body.

Nursing and pharmacy students learn it as an introduction to pediatric dosing, and it still shows up as a quick sanity check in settings without a pediatric-specific dose chart. It only needs the child's weight and the normal adult dose to work.

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