How to Calculate Body Surface Area (BSA)

BSA (m2) = sqrt((Height cm x Weight kg) / 3600) Example: 175cm tall, 75kg BSA = sqrt((175 x 75) / 3600) = sqrt(13125 / 3600) = sqrt(3.6458) = 1.909 m2 Average adult BSA (reference): Adult male: approximately 1.9 m2 Adult female: approximately 1.6 m2 Newborn: approximately 0.25 m2

DuBois and DuBois (1916, original formula): BSA = 0.007184 x Height^0.725 x Weight^0.425 (Height in cm, Weight in kg) Example: 175cm, 75kg: = 0.007184 x 175^0.725 x 75^0.425 = 0.007184 x 59.13 x 8.975 = 3.811 -- wait, need to check... = 0.007184 x 59.13 x 8.975 = 3.811? Let me recalculate 175^0.725: ln(175) = 5.165, x0.725 = 3.744, e^3.744 = 42.26 75^0.425: ln(75) = 4.317, x0.425 = 1.835, e^1.835 = 6.265 BSA = 0.007184 x 42.26 x 6.265 = 1.902 m2 Haycock formula (preferred for children): BSA = 0.024265 x Height^0.3964 x Weight^0.5378 For paediatric dosing, the Haycock formula is recommended as it performs better at lower heights and weights.

Chemotherapy dosing: Most cytotoxic drugs are dosed in mg/m2 of BSA Carboplatin 400mg/m2: for BSA 1.9 m2 = 760mg dose (Much more precise than weight-based dosing for toxic drugs) Burn assessment (Rule of Nines): Head and neck: 9% BSA Each arm: 9% BSA Chest: 9% | Abdomen: 9% | Upper back: 9% | Lower back: 9% Each thigh: 9% | Each lower leg: 9% Perineum: 1% For a 1.9 m2 BSA adult, a burn covering the entire right arm: Burn area = 9% x 1.9 m2 = 0.171 m2 Fluid resuscitation for burns (Parkland formula): IV fluid in first 24h = 4 x weight (kg) x % burn surface area (Not directly BSA-based but uses burn percentage of BSA)