## Rule of Nines for Body Surface Area Estimation **Key Point:** The Rule of Nines is the most widely used method for rapid estimation of total body surface area (TBSA) affected by burns in adults. ### Adult Distribution (Rule of Nines) | Body Region | Percentage of TBSA | | --- | --- | | Head and Neck | 9% | | Each Upper Limb (anterior + posterior) | 9% | | Each Lower Limb (anterior + posterior) | 18% | | Anterior Trunk | 18% | | Posterior Trunk | 18% | | Genitalia | 1% | | **Total** | **100%** | **High-Yield:** The head and neck together account for exactly **9%** of TBSA in adults. This is a frequently tested fact in forensic medicine and burn management. **Clinical Pearl:** The Rule of Nines becomes less accurate in children under 10 years; the Lund and Browder chart is preferred in pediatric burns because children have proportionally larger heads (18% vs 9% in adults). **Mnemonic:** **"9-18-36-1"** — Head 9%, Each arm 9%, Each leg 18%, Trunk 36%, Genitalia 1%.
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