In the Field
Rule of Nines is the field math for burn TBSA. Each arm is 9 percent. Each leg is 18 percent. The torso anterior is 18 percent, posterior is 18 percent. The head is 9 percent. The perineum is 1 percent. Add up the involved regions, round to the nearest 10 percent, and that is your TBSA. From there, the Rule of Ten gives you the initial fluid rate. The Rule of Palm (the casualty's palm equals roughly 1 percent of their TBSA) handles small scattered burns that do not fit the Rule of Nines regions.
Common Mistake
Including superficial (first-degree) burns in the TBSA calculation. Only partial-thickness (second-degree) and full-thickness (third-degree) burns count toward TBSA for fluid resuscitation calculations. Sunburn-type erythema without blistering is not part of the calculation. The other mistake is using the adult Rule of Nines unmodified in pediatric casualties; the proportions shift significantly. Pediatric heads represent a larger TBSA percentage and pediatric legs a smaller percentage; the Lund-Browder chart adjusts for age.
Technical Detail
Adult Rule of Nines distribution: head and neck 9 percent; each upper extremity 9 percent (4.5 percent anterior, 4.5 percent posterior); anterior trunk 18 percent (chest 9, abdomen 9); posterior trunk 18 percent; each lower extremity 18 percent (9 percent anterior, 9 percent posterior); perineum 1 percent. Total 100 percent. Pediatric variation requires age-specific adjustment (Lund-Browder chart): infant head approximately 18 percent, decreasing with age; infant legs approximately 13.5 percent each, increasing with age. Adult proportions are typically achieved by age 10 to 15. TCCC 2026 specifies estimation to the nearest 10 percent. Only second-degree (partial-thickness) and third-degree (full-thickness) burns are counted. The Rule of Palm (patient's palm including digits equals approximately 1 percent of their TBSA) supplements the Rule of Nines for irregular or scattered burns.
