Body Surface Area (BSA) Calculator
Enter your height and weight to get your body surface area in square metres, computed by the five major published formulas — Mosteller (clinical default), DuBois, Haycock, Gehan & George and Boyd.
Body surface area
2.0380 m²
- In square feet
- 21.9366 ft²
- In square centimetres
- 20380 cm²
- Height used
- 178.00 cm
- Weight used
- 84.000 kg
- Mosteller (1987) — clinical default
- 2.0380 m²
- DuBois & DuBois (1916)
- 2.0218 m²
- Haycock (1978) — paediatric
- 2.0508 m²
- Gehan & George (1970)
- 2.0509 m²
- Boyd (1935)
- 2.0544 m²
BSA via Mosteller (1987) — clinical default. Mosteller is the clinical default (used for chemotherapy dosing): BSA = √(H·W/3600) with H in cm and W in kg. The other four formulas use fitted power laws — DuBois (historical), Haycock (paediatric), Gehan & George, and Boyd. Typical adult BSA falls between 1.5 and 2.2 m².
How to use this calculator
Pick which formula you want to use as the headline result — Mosteller is the clinical default and the one most chemotherapy dosing nomograms are built around, so leave it on Mosteller unless you have a specific reason to pick another. Enter your height in centimetres or inches and your weight in kilograms or pounds; the calculator converts both to SI internally using the exact NIST factors (1 inch = 2.54 cm; 1 lb = 0.453 592 37 kg). The headline number is your BSA in m² from the selected formula; the breakdown converts that to square feet and square centimetres, echoes the height and weight in SI for transparency, and then runs all five formulas so you can see how much they disagree on your specific anthropometry — usually within ±5 %, but more for outliers.
How the calculation works
Body surface area is the total external area of skin covering the body and is used in medicine as a proxy for metabolic rate, drug distribution volume, cardiac index and burn extent — most chemotherapy doses are expressed in mg/m² rather than mg/kg precisely because BSA tracks drug clearance more reliably than mass does. Direct measurement (covering a body in tape or paper) is impractical, so all clinical BSAs are computed from height and weight using fitted formulas. Mosteller (1987) is the modern default: BSA = √(H·W / 3600) with H in cm and W in kg — a deliberately simple square-root form that matches DuBois to within 1 % for most adults and is trivial to do at the bedside. DuBois & DuBois (1916) is the original power-law fit (BSA = 0.007184·W^0.425·H^0.725) derived from coating nine subjects in moulding paper. Haycock (1978) extended the fit to paediatric subjects (0.024265·W^0.5378·H^0.3964). Gehan & George (1970) re-fitted on 401 subjects (0.0235·W^0.51456·H^0.42246). Boyd (1935) used a log-corrected exponent that varies with weight. The disagreement between formulas is most visible at extremes — very small children and very obese adults — and is the reason clinicians often cap chemotherapy BSA at 2.0 m² regardless of which formula is used.
Worked example
Take an adult who is 178 cm tall (5 ft 10 in) and weighs 84 kg (185 lb). Mosteller: √(178 × 84 / 3600) = √4.1533 = 2.038 m². DuBois: 0.007184 × 84^0.425 × 178^0.725 ≈ 2.022 m². Haycock: 0.024265 × 84^0.5378 × 178^0.3964 ≈ 2.051 m². Gehan & George: 0.0235 × 84^0.51456 × 178^0.42246 ≈ 2.045 m². Boyd: 0.0003207 × 178^0.3 × 84000^(0.7285 − 0.0188·log₁₀ 84000) ≈ 2.034 m². All five agree to within 1.5 % — Mosteller (2.04) is the value most chemotherapy nomograms would use. Now take a child who is 100 cm tall and weighs 30 kg: Mosteller = √(100 × 30 / 3600) = √0.833 = 0.913 m². Haycock — preferred for paediatrics — gives 0.938 m². The 3 % gap is exactly the kind of paediatric correction Haycock was fitted to capture.
Frequently asked questions
Which BSA formula should I use?
For most adult clinical use, Mosteller. It is the formula most chemotherapy dosing nomograms are built around, it is trivial to compute at the bedside (a single square root) and it matches the older DuBois value to within about 1 % across the normal adult range. For paediatric patients, Haycock is the preferred choice — it was fitted on a population that included children and gives more accurate values below about 50 kg. DuBois remains the historical reference and is what older nomograms and textbook tables are based on. Gehan & George and Boyd are alternative fits used in specific oncology and burn-care protocols. In adults of normal weight all five formulas agree to within 5 %; differences widen at the extremes of weight and height.
Why is BSA used for drug dosing instead of body weight?
Many physiological processes — basal metabolic rate, glomerular filtration rate, cardiac output, blood volume — scale more closely with surface area than with mass. Chemotherapy agents in particular have narrow therapeutic windows and are cleared by mechanisms (renal filtration, hepatic metabolism) whose capacity tracks BSA better than it tracks weight. Dosing in mg/m² therefore reduces inter-patient variability in drug exposure compared with mg/kg. There are exceptions — some monoclonal antibodies and paediatric anaesthetic agents are still dosed on weight — but for cytotoxic chemotherapy, mg/m² remains the standard.
What is a normal body surface area?
The average adult BSA is about 1.7 m² for women and 1.9 m² for men. The full normal adult range is roughly 1.5 to 2.2 m². Children scale roughly with growth: a newborn is around 0.25 m², a one-year-old around 0.45 m², a five-year-old around 0.75 m². Very large adults can exceed 2.5 m². Chemotherapy dosing is often capped at 2.0 m² regardless of measured BSA, because the linear dose-response relationships used to derive the original mg/m² doses were calibrated on patients within the normal range.
How accurate are computed BSAs compared to direct measurement?
Computed BSAs agree with direct measurement (the historical "coating" method) to within about 5 % for adults of normal build. They are less accurate at the extremes — very obese, very thin or very young patients can have measured BSAs that differ from computed by 10 % or more. For most clinical purposes, that error is dwarfed by inter-patient pharmacokinetic variability, so any of the five published formulas is fit for purpose. The choice between them matters most at the population extremes and for drugs with the narrowest therapeutic windows.
Why does Mosteller use exactly 3600 in the divisor?
It is a numerical coincidence that makes the formula easy to remember and compute mentally. Mosteller derived his simplified form by fitting a square-root model to the same data DuBois used, and 3600 happens to be the constant that makes the fit closest to DuBois across the adult range. There is no biological meaning to the number — it is purely the result of regression. The square-root form is biologically motivated though: surface area scales as the square of a linear dimension while mass scales as the cube, so a product of linear height and mass under a square root captures the geometric relationship between volume and surface area for a body of roughly constant density.
Is BSA the same as Body Mass Index (BMI)?
No. BMI (weight in kg divided by height in metres squared) is a ratio used as a rough proxy for adiposity. BSA is an estimate of the actual external surface area of the body in square metres. BMI tells you whether someone is underweight, normal, overweight or obese for their height; BSA tells you a physiologically meaningful absolute quantity that scales with metabolic capacity and is used for drug dosing. A 178 cm 84 kg adult has BMI ≈ 26.5 (overweight category) and BSA ≈ 2.04 m² (normal adult range). They measure different things for different purposes.