Body Surface Area (BSA) Calculator
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Body surface area (BSA) is a mathematical estimate of the external surface of the human body. Enter height and weight to compare four established equations: Mosteller, Du Bois and Du Bois, Haycock, and Gehan–George. Metric and imperial measurements are accepted, including fractional inches. The calculation happens in your browser tab. Results are educational estimates only and must not be used independently for diagnosis, medicine or chemotherapy dosing, fluid treatment, or burn assessment.
How to estimate body surface area
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Choose a measurement system
Select centimetres and kilograms, or feet, inches and pounds. Imperial values are converted with exact standard conversion factors.
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2
Enter measured height and weight
Use current values and include fractional inches when needed, such as 5 feet 6 1/2 inches.
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3
Compare four estimates
Review the BSA in square metres from Mosteller, Du Bois, Haycock and Gehan–George without treating one as clinical advice.
What the four BSA formulas calculate
Each equation estimates body surface area in square metres from height H in centimetres and weight W in kilograms:
| Formula | Equation |
|---|---|
| Mosteller | √((H × W) / 3600) |
| Du Bois and Du Bois | 0.007184 × H^0.725 × W^0.425 |
| Haycock | 0.024265 × H^0.3964 × W^0.5378 |
| Gehan–George | 0.0235 × H^0.42246 × W^0.51456 |
Mosteller published the simplified square-root equation in 1987. The older Du Bois equation was developed from a small early sample. Haycock and colleagues validated their equation using geometric measurements from premature infants through adults, while Gehan and George derived another height–weight relationship from a larger sample. Because their coefficients and exponents differ, the answers are close but not identical.
Worked example
For a height of 170 cm and a weight of 70 kg:
- Mosteller:
√((170 × 70) / 3600)= 1.8181 m² - Du Bois: 1.8097 m²
- Haycock: 1.8257 m²
- Gehan–George: 1.8313 m²
Do not round height or weight before the calculation. The tool keeps full precision internally and rounds only the displayed results.
Limits and appropriate use
BSA is an estimate rather than a direct measurement. Equation differences may become more important at unusual body sizes, and the choice of formula depends on the clinical or research protocol. A BSA result is not a diagnosis and is not enough information to select a medicine dose, chemotherapy dose, fluid plan, or treatment. It is also unrelated to the percentage of body area affected by a burn.
Primary references include Mosteller’s 1987 paper, the original Du Bois article, and the Haycock validation study. The US Environmental Protection Agency’s Exposure Factors Handbook provides broader context on body surface area estimates.
Frequently Asked Questions
Body surface area is an estimate of the external surface of the body, expressed here in square metres. These equations infer it from height and weight rather than measuring the skin directly.
That depends on the protocol or purpose. Mosteller is simple and widely recognized, while Du Bois, Haycock and Gehan–George use different fitted exponents. A clinician or protocol should specify the equation when the result affects care.
No. Do not calculate or change a dose from this tool. Dosing requires the correct protocol, patient-specific clinical information, verification and professional oversight; BSA is only one possible input.
No. Estimated total body surface area in m² is different from total body surface area burned, which is a percentage assessed with burn-specific methods by trained clinicians.
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