Pediatric Medication Dosage Calculator
Estimates a child's safe medication dose from the known adult dose using Clark's, Young's, or Fried's rule. Use it when a pediatric-specific dose isn't listed and you need a weight- or age-based starting point.
About this calculator
Three classical rules approximate a child's dose as a fraction of the standard adult dose. Clark's Rule uses body weight: Child Dose = (childWeight / 70) × adultDose. Young's Rule uses age: Child Dose = (childAge / (childAge + 12)) × adultDose. Fried's Rule (often used for infants) uses age in months scaled to 150: Child Dose = (childAge / 150) × adultDose. Each rule produces a different estimate because children's pharmacokinetics vary with both size and developmental stage. Clark's Rule is generally preferred when an accurate weight is available, while Young's Rule works well for children aged 2–12 when weight is unknown. Always verify the result with a pharmacist or prescriber before administering any medication.
How to use
Suppose a 6-year-old child weighs 22 kg and the standard adult dose is 500 mg. Using Clark's Rule: Child Dose = (22 / 70) × 500 = 0.314 × 500 = 157 mg. Using Young's Rule: Child Dose = (6 / (6 + 12)) × 500 = (6 / 18) × 500 = 0.333 × 500 = 167 mg. Enter the child's weight (22 kg), age (6 years), adult dose (500 mg), and select your preferred method. The calculator instantly returns the estimated dose. Always round to a practical measurable amount and confirm with a healthcare provider.
Frequently asked questions
What is the difference between Clark's Rule and Young's Rule for pediatric dosing?
Clark's Rule bases the dose on the child's weight relative to an average adult weight of 70 kg, making it more accurate when the child's weight is known. Young's Rule relies solely on age, which is useful when a scale isn't available but is less precise because children of the same age can vary significantly in size. For infants under 2 years, neither rule is recommended without clinical guidance, and Fried's Rule or weight-based mg/kg dosing is preferred. Always treat these rules as rough estimates rather than definitive prescriptions.
When should I use a weight-based pediatric dose calculator instead of age-based formulas?
Weight-based dosing (mg/kg) is considered the gold standard in modern pediatric pharmacology because it directly accounts for individual body size. Age-based rules like Young's and Fried's were developed before accurate pediatric drug studies existed and can under- or over-dose children who are significantly above or below average weight for their age. You should use weight-based dosing whenever the child's weight is reliably known and a specific mg/kg guideline is available on the drug label or formulary. This calculator's Clark's Rule option approximates weight-based dosing from the adult dose when no mg/kg reference is published.
Are these pediatric dosage formulas safe for infants under 1 year old?
These classical rules are not designed for neonates or infants under 12 months and should not be used as the sole basis for dosing in that age group. Infant metabolism, kidney function, and drug distribution differ dramatically from older children, making simple fraction-of-adult-dose approaches unreliable. Fried's Rule (age in months / 150) is sometimes used as a rough guide for older infants but still carries significant error margins. For any infant, dosing must be determined by a pediatrician or clinical pharmacist using weight-based protocols specific to the drug in question.