Free BSA calculator comparing Mosteller, Du Bois, Haycock, Gehan-George, and Boyd formulas side by side in m² for dosing and clinical use.
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Body Surface Area is used in medicine to calculate drug dosages, determine burn severity, and assess body size. This calculator computes all five standard formulas at once — Mosteller (the clinical default), Du Bois, Haycock, Gehan-George, and Boyd — so you can compare them side by side instead of picking just one.
BSA measures total skin surface area in square meters. Unlike BMI, it accounts for both height and weight to estimate actual body size, and average adult BSA is about 1.7–1.9 m². BSA is preferred over weight for dosing many medications because it better correlates with blood volume, cardiac output, and metabolic rate. The five supported formulas use the same height and weight but different exponents: Du Bois (1916) is the historical standard; Mosteller (1987) is a simple square-root form used clinically; Haycock (1978) and Gehan-George (1970) were fitted for children; and Boyd (1935) uses a weight-dependent exponent and typically returns a slightly lower value.
Mosteller Formula (Clinical Default)
Calculate drug doses prescribed per square meter (mg/m²).
Divide cardiac output by BSA to compare across patients.
Determine the percentage of body surface affected.
Normalize kidney function estimates to standard 1.73 m².
Complement BMI with a true body-size measurement.
Dose chemotherapy and other drugs prescribed in mg/m².
Estimate burn severity and fluid resuscitation needs.
Normalize cardiac output to body size (L/min/m²).
Adjust GFR and creatinine clearance to standard BSA.
Compare metabolic and physiologic data across body sizes.
Mosteller is the most widely used because it is simple and accurate, so it is the default here. Du Bois is the classic reference formula; Haycock and Gehan-George were fitted to include children; Boyd is an older formula that runs slightly lower. Your healthcare provider or protocol may specify which to use — this tool shows all five so you can compare.
Boyd (1935) is BSA = 0.0003207 × Height_cm^0.3 × Weight_grams^(0.7285 − 0.0188 × log₁₀(Weight_grams)), with weight in grams. The weight exponent itself depends on weight, so Boyd curves differently from the others at body-size extremes, though for typical adults it agrees closely. For 70 kg and 175 cm it gives about 1.85 m², matching Mosteller and Du Bois.
Average adult BSA is about 1.7 m² for women and 1.9 m² for men, and typically ranges from 1.5–2.2 m² in adults. Children have lower BSA proportional to their size — roughly 0.8–1.3 m² for ages 5–12.
BSA correlates better with blood volume, cardiac output, and organ size than weight alone. This provides more accurate dosing, especially for drugs with narrow safety margins like chemotherapy, which is why many are prescribed in mg/m².
The 'Rule of Nines' divides body surface into percentages, and BSA helps calculate fluid resuscitation needs — burns over about 20% of body surface require aggressive IV fluids using formulas like Parkland.