Body Surface Area Calculator

About the Body Surface Area Calculator

A body surface area (BSA) calculator estimates the total skin surface area of a human body in square metres using height and weight, applying the Mosteller and DuBois formulas — the two most widely used clinical standards. BSA is a critical parameter in medicine because it correlates better than body weight with metabolic rate, cardiac output, and drug distribution volume for many medications. Chemotherapy drug doses are routinely calculated in mg/m² of BSA rather than mg/kg of body weight, because this reduces inter-patient variability in drug exposure. The Mosteller formula (BSA = √(H_cm × W_kg / 3600)) is used in most modern clinical practice due to its simplicity; the DuBois formula (0.007184 × H_cm^0.725 × W_kg^0.425), published in 1916, was historically standard and remains in use for comparison. Average BSA values: adult male ~1.9 m², adult female ~1.6 m², reference value used in many drug calculations = 1.73 m². This calculator is essential for oncologists, clinical pharmacists, burn specialists, intensivists, and medical students.

How It Works

Mosteller: BSA (m²) = √(H_cm × W_kg / 3600). Equivalent: √((H_in × W_lb) / 3131). DuBois: BSA (m²) = 0.007184 × H_cm^0.725 × W_kg^0.425. Haycock (often used in paediatrics): 0.024265 × H_cm^0.3964 × W_kg^0.5378. Example — 175 cm, 70 kg male. Mosteller: √(175 × 70 / 3600) = √(12250/3600) = √3.403 = 1.844 m². DuBois: 0.007184 × 175^0.725 × 70^0.425 = 0.007184 × 54.89 × 7.267 = 1.868 m². The two formulas agree within 1.3% for this typical adult. Chemotherapy dosing example: drug dosed at 50 mg/m². For 1.85 m² BSA: dose = 50 × 1.85 = 92.5 mg (rounded to nearest 10 mg or 5 mg per protocol). Burn rule of nines: head = 9%, each arm = 9%, chest = 18%, abdomen = 18%, each leg = 18%, perineum = 1% = total 100% BSA.

Tips & Best Practices

• ✓For chemotherapy dosing, most centres cap BSA at 2.0-2.2 m² for obese patients, using actual body weight for some agents and adjusted or ideal weight for others. Always follow the specific protocol or institutional guidelines rather than applying BSA mechanically — some drugs use flat dosing, weight-based dosing, or capped BSA.
• ✓The "reference man" BSA of 1.73 m² (170 cm, 70 kg) is used as a normalisation factor in cardiac physiology. Cardiac index = Cardiac output (L/min) / BSA (m²). Normal cardiac index is 2.5-4.0 L/min/m². Reporting cardiac output per BSA removes the effect of body size on the measurement.
• ✓Paediatric dosing: the Haycock formula (published 1978) is recommended for children because it was developed from measurements of subjects across a wider age and size range. Paediatric drug doses are often expressed per m² for chemotherapy and per kg for other medications — check which metric the prescribing reference uses.

Who Uses This Calculator

Oncologists and clinical pharmacists calculating chemotherapy drug doses from patient height and weight. Burn unit clinicians estimating percent body surface area burned for fluid resuscitation calculations (Parkland formula). Medical students and nursing students learning BSA-based dosing principles and practising clinical calculations. Intensivists calculating cardiac index from measured cardiac output and patient BSA.