When a weight-based dose isn’t available, older rules estimate a child’s dose from the adult dose — Clark’s rule (by weight) and Young’s rule (by age). Both are one short formula.
The example
Adult 500 mg, 50 lb child.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 500 × 50 | — |
| 3 | ÷ 150 | → 167 mg |
The formula
The formula:
How it works
How it works:
- Clark’s rule:
adult_dose × child_weight_lb / 150— based on a 150 lb reference adult. - Young’s rule (age):
adult_dose × age / (age + 12)for children 1–12. - These are historical approximations — modern practice prefers weight-based (mg/kg) dosing.
- Use them to understand the relationship; confirm real doses against current references.
Educational use only. These are general Excel formulas for learning spreadsheet techniques — not medical advice or a substitute for clinical judgment, professional guidelines, or verified dosing references. Always confirm calculations against authoritative sources and institutional protocols.
Try it: interactive demo
Adult dose, child weight (lb), age (yr).
Variations
Young's rule (age)
For ages 1–12:
Weight-based (preferred)
If mg/kg known:
Fried's rule (infants)
By months:
Pitfalls & errors
Approximations. Clark’s/Young’s rules are historical — weight-based mg/kg dosing is the modern standard.
Right units. Clark’s uses pounds; Young’s uses years.
Always verify. Confirm pediatric doses against current clinical references.
Practice workbook
Frequently asked questions
How do I estimate a pediatric dose in Excel?
Which rule should I use?
What units do the rules use?
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