BSA Calculator (Body Surface Area)
Enter your height and weight to estimate your body surface area in square metres, compared across four validated formulas.
A typical adult's body surface area is about 1.71 m² for women and 1.91 m² for men, and the four validated formulas agree within about 0.7% at that size.
What body surface area tells you
Body surface area (BSA) estimates the total area of your skin in square metres from your height and weight. It matters because many physiological quantities — cardiac output, kidney filtration, drug clearance — scale better with surface area than with weight alone. That's why chemotherapy doses are prescribed per m² and kidney function (eGFR) is reported per 1.73 m² of body surface. Unlike BMI, BSA isn't a health classification — it's a scaling measurement.
The default here is the Mosteller formula — the square root of height times weight divided by 3,600 — which became the clinical favourite for its simplicity. The classic Du Bois formula dates to 1916, fitted to direct tape measurements of just nine people, yet it agrees with Mosteller within about 1–2% for typical adults. For body-composition questions, pair BSA with lean body mass and FFMI.
Four formulas compared (180 cm, 80 kg)
| Formula (year) | Equation | BSA |
|---|---|---|
| Mosteller (1987) | √(height × weight ⁄ 3600) | 2.00 m² |
| Du Bois (1916) | 0.007184 × h0.725 × w0.425 | 2.00 m² |
| Haycock (1978) | 0.024265 × h0.3964 × w0.5378 | 2.01 m² |
| Gehan–George (1970) | 0.0235 × h0.42246 × w0.51456 | 2.01 m² |
For a typical adult the four validated formulas agree within ~0.7%. They diverge more at the extremes — young children, very tall or very heavy adults — and Du Bois tends to overestimate in people with obesity.
Limits worth knowing
BSA is an estimate from two numbers; it can't see body composition, and every formula carries the fingerprint of the population it was fitted on. Results are shown to two decimal places by clinical convention — more precision than that would be false. And one limit above all: this tool is educational. It must never be used to calculate or adjust medication doses — that's a decision for clinicians working from protocols, not from a web page.
Sources: Mosteller, NEJM (1987); Du Bois & Du Bois, Arch Intern Med (1916); Haycock, J Pediatr (1978); Gehan & George, Cancer Chemother Rep (1970); StatPearls (NCBI); Sacco et al. UK average-BSA study; Heaf, on the 1.73 m² convention. Educational estimates, not medical advice.
Frequently asked questions
What is a normal body surface area?
In a large UK adult study using the Du Bois formula, men averaged about 1.91 m² and women about 1.71 m². More recent US general-population data (NHANES 2011–2014) put averages higher — roughly 2.06 m² for men and 1.83 m² for women. A newborn is around 0.24 m². "Normal" spans a wide range with body size.
Which BSA formula should I use?
Mosteller is the modern default — simple, and it agrees with the classic Du Bois formula to within about 1–2% for typical adults. Du Bois remains the traditional reference in adult oncology, while Haycock and Gehan–George were validated across infants, children and adults. For a typical adult all four land within about 0.7% of each other.
What is BSA actually used for?
Medicine uses body surface area to scale physiology and drug doses — chemotherapy doses are commonly prescribed per m², and kidney function (eGFR) is indexed to a standard 1.73 m² body. It's a better scaling factor than weight alone for many purposes because metabolic processes track surface area more closely than mass.
Why 1.73 m²?
The 1.73 m² used to index eGFR is a normalization constant — the average BSA of a 1920s US cohort of 25-year-olds. It was described by later researchers as an essentially arbitrary historical choice, and modern adults average larger, but it remains the universal standard so results stay comparable.
Can I use this to check a medication dose?
No. This calculator is educational only. Dose calculations — especially chemotherapy — involve clinical judgment, protocols, and sometimes deliberate adjustments that no online tool can capture. If you have questions about a dose, ask your prescriber or pharmacist.
Sources
- Mosteller RD — Simplified calculation of body-surface area (N Engl J Med, 1987) — Mosteller BSA formula, original paper
- Du Bois D & Du Bois EF — A formula to estimate surface area if height and weight be known (1916; Nutrition, 1989) — Du Bois BSA formula, 1916
- Haycock GB et al. — Geometric method for measuring body surface area (J Pediatr, 1978) — Haycock height-weight BSA formula
- Gehan EA & George SL — Estimation of human body surface area from height and weight (Cancer Chemother Rep, 1970) — Gehan-George BSA formula
The thresholds and formulas used by this calculator follow the primary sources above. This tool provides general information, not personalised medical advice.