Clark's Rule Calculator (Educational & Exam Reference)
Estimates paediatric dose from adult dose using weight in pounds (lb) or kg for academic/GPAT examination preparation.
⚠️ Educational Calculation & Clinical Safety Safeguard: EDUCATIONAL / HISTORICAL FORMULA ONLY: In clinical practice, always use validated drug-specific mg/kg or BSA paediatric dosing. Educational calculations do not replace clinician assessment, patient-specific laboratory monitoring, or institutional prescribing protocols.
Interactive Calculator
Allowed physiological/compounding range: 2 to 70 kg
Allowed physiological/compounding range: 1 to 5000 mg
Calculated Output (mg)
---
---
Step-by-Step Mathematical Derivation & Explanation:
Validated Formula & Conversion Rules
Clark's Rule: Child Dose = [Weight in lb / 150] × Adult Dose (where Weight in lb = kg × 2.2) ≈ [Weight in kg / 68.18] × Adult DoseWorked Clinical Example
20 kg child (44 lb), Adult Dose 500 mg: Child Dose = (44 / 150) × 500 = 146.67 mg.
Rounding Rules, Clinical Interpretation, Assumptions & Known Limitations
- 1. Purpose: Estimates paediatric dose from adult dose using weight in pounds (lb) or kg for academic/GPAT examination preparation.
- 2. Required Inputs & Validated Units: Child Weight (kg, range 2–70), Standard Adult Dose (mg, range 1–5000)
- 3. Output Unit:
mg - 4. Result Interpretation Notes: Academic and GPAT examination reference for Clark's Rule (Weight in lb / 150 × Adult Dose).
- 5. Rounding Guidance: For examination MCQs, note whether 1 kg = 2.2 lb (150 lb ≈ 68 kg) or 70 kg denominator is specified.
- 6. Mathematical & Clinical Assumptions: Assumes a historical 150 lb (68 kg) reference adult weight and linear weight proportionality.
- 7. Known Limitations & Contraindications to Formula Use: Historical rule for academic exam preparation only; modern paediatric clinical practice uses drug-specific mg/kg or mg/m² dosing.
- 8. Supporting Compendial & Clinical References: Indian Pharmacopoeia (IP 2022), National Formulary of India (NFI), British National Formulary (BNF), and NCBI Bookshelf Clinical Pharmacology Compendia.