Body Surface Area Calculator

Enter your height and weight; the tool returns body surface area using both the Du Bois and Mosteller formulas. Switch between metric and imperial units freely — the conversion happens before the BSA calculation.

BSA shows up in clinical contexts: chemotherapy dosing, cardiac index, burn-percentage estimation. Mosteller is the formula most clinicians prefer because it's quicker to compute by hand; Du Bois is older but still appears in legacy protocols and some textbooks.

The two formulas typically agree to within 1–2%. Where they disagree, the difference is largest at the extremes of body composition — pediatric, very small adults, and very large adults.

Mosteller formula: BSA (m²) = sqrt(height(cm) × weight(kg) / 3600). Du Bois: BSA (m²) = 0.007184 × height(cm)^0.725 × weight(kg)^0.425. Mosteller is preferred clinically because it's faster mental math (sqrt of a product), and it agrees with Du Bois to within 1-2% across normal adult ranges. The Du Bois formula dates to 1916 from a small sample of patients. Mosteller appeared in 1987 with a derivation chosen partly because it could be done with a pocket calculator at the bedside.

Worked example. A 175 cm, 75 kg adult: Mosteller BSA = sqrt(175 × 75 / 3600) = sqrt(3.646) = 1.91 m². Du Bois BSA = 0.007184 × 175^0.725 × 75^0.425 = 0.007184 × 41.64 × 6.43 = 1.92 m². Two formulas, same essential answer, 0.5% difference. For chemotherapy dosing where the order is in mg/m², the difference is in the third significant figure — clinically irrelevant for almost any drug. For research where you need consistent methodology across studies, pick one formula and stick with it.

Where the formulas disagree. Pediatric and small adult cases (<60 kg, <150 cm) can show 3-5% differences. Very large body sizes (>120 kg) can show similar gaps. Boyd, Haycock, and Gehan formulas were developed specifically for pediatric use and may agree better with each other than either does with Mosteller in that range. The tool exposes all four formulas; clinicians should pick the one their institution uses by protocol.

Known limitations of BSA-based dosing. BSA was adopted as a dosing surface because it correlates with metabolic rate and organ function, but it doesn't account for body composition. A bodybuilder and a sedentary person of identical height and weight have very different lean body mass, hepatic metabolism, and renal function — yet BSA-based dosing treats them identically. Modern oncology has shifted away from BSA dosing for many drugs, using fixed dosing or body-weight-only formulas instead. The tool computes BSA accurately; whether BSA is the right input for your dose is a separate question your protocol answers.