About the pediatric dose calculator
This calculator estimates a child's medication dose from a known adult dose using three long-standing pharmacy teaching formulas: Clark's Rule, Young's Rule, and the Mosteller body surface area (BSA) method. All three scale an adult dose down for a smaller body, using a different single measurement (weight, age, or a height-and-weight composite) as the scaling factor.
The three formulas
- Clark's Rule: child dose = (weight in pounds / 150) x adult dose. It assumes a 150 lb reference adult and scales linearly with the child's weight.
- Young's Rule: child dose = (age / (age + 12)) x adult dose. It uses only age, so it can misestimate dose for children whose weight is unusually high or low for their age.
- Mosteller BSA method: body surface area (m²) = square root of (height in cm x weight in kg / 3600); child dose = (child BSA / 1.73) x adult dose, using 1.73 m² as the reference adult body surface area.
Interpreting the three estimates
The three methods will rarely agree exactly, because each uses different information. The BSA method is generally regarded as the most physiologically sound of the three ratio rules since it incorporates both height and weight, while Clark's and Young's Rules use only one variable each. A wide spread between the three numbers usually means the child's height-to-weight proportions differ from the "average" child implied by the age-only or weight-only rule.
Important disclaimer
None of these three rules is the clinical standard of care. Modern pediatric dosing is normally based on drug-specific milligrams-per-kilogram (mg/kg) guidance from a pharmacology reference, which accounts for the specific medication's therapeutic window and the child's weight directly. This tool performs the standard arithmetic of these three textbook formulas for educational purposes only; it does not diagnose, treat, or recommend a dose. Always confirm any pediatric medication dose with a licensed clinician or pharmacist before it is given.