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Paediatric Dosage Calculator

Calculate children's medication doses based on weight or age.

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Formula

Dose = (Child Weight / Adult Weight) * Adult Dose (Clark's Rule)

Calculates safe medication doses for children using established clinical rules.

Worked Example

Child 20kg, Adult 70kg, Adult Dose 500mg -> 143mg.

Pediatric Dosing Rules

Children are not just "small adults"; their metabolism and body composition differ. While weight-based dosing (mg/kg) is standard today, historical rules like Clark's and Young's provide estimates based on adult doses.
  • Clark's Rule: Dose = (Weight in kg / 70) × Adult Dose OR (Weight in lbs / 150) × Adult Dose
  • Young's Rule: Dose = [Age / (Age + 12)] × Adult Dose (typically for ages 1-12)
  • Modern practice prefers precise mg/kg or mg/m² dosing for most medications
  • Always verify pediatric doses with a pharmacist or specialist reference (e.g., Harriet Lane)

This tool provides a mathematical estimate. Pediatric medications must be prescribed by a qualified healthcare professional who considers the child's full clinical picture.

You can also calculate changes using our Corrected Age Calculator or IV Drip Rate Calculator.

Frequently Asked Questions

What is Clark's Rule?

Clark's Rule is a medical formula used to estimate a child's dose of medication based on their weight compared to an average adult weight of 70kg (or 150lbs).

When is Young's Rule used?

Young's Rule uses a child's age to estimate medication dosage. It is generally considered less accurate than weight-based methods because children's weights vary significantly at the same age.

Can I use this for all medications?

No. Many medications (like antibiotics or chemo) have very specific mg/kg dosing that cannot be estimated by these general rules.

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