Free surgery & anesthesia tool
Body Surface Area Calculator (BSA, Mosteller)
Body surface area (BSA) is estimated from height and weight. The Mosteller formula is the simplest: BSA in m² equals the square root of (height in cm × weight in kg ÷ 3,600). A person who is 170 cm and 70 kg has a BSA of √(11,900 ÷ 3,600) = 1.82 m². This calculator also shows Du Bois, Haycock, Gehan-George and Boyd side by side, in cm/kg or ft/in/lb.
Prepared by Prospyr · Reviewed October 3, 2026 · Free, no sign-up, runs in your browser
Body surface area (Mosteller)
1.79m²
Height 170.2 cm, weight 68 kg.
| Formula | m² |
|---|---|
| Mosteller (1987) | 1.793 |
| Du Bois & Du Bois (1916) | 1.789 |
| Haycock (1978) | 1.799 |
| Gehan & George (1970) | 1.806 |
| Boyd (1935) | 1.807 |
A math aid. BSA is an estimate from height and weight; confirm which formula your protocol or label specifies. Dosing decisions belong to the treating provider.
BSA formulas: Mosteller, Du Bois, Haycock, Gehan-George and Boyd
All five formulas turn height (H, cm) and weight (W, kg) into square meters. They differ in the constants fitted to the groups each author measured.
| Formula | Year | Equation |
|---|---|---|
| Mosteller | 1987 | √(H × W ÷ 3,600) |
| Du Bois & Du Bois | 1916 | 0.007184 × W^0.425 × H^0.725 |
| Haycock | 1978 | 0.024265 × W^0.5378 × H^0.3964 |
| Gehan & George | 1970 | 0.0235 × W^0.51456 × H^0.42246 |
| Boyd | 1935 | 0.0003207 × H^0.3 × g^(0.7285 − 0.0188 × log10 g), g = weight in grams |
The tool defaults to Mosteller, the body surface area calculator most people search for, and lists the others so you can see how much the choice matters.
Worked example: the Mosteller formula by hand
A patient is 170 cm tall and weighs 70 kg.
- Multiply height by weight: 170 × 70 = 11,900.
- Divide by 3,600: 11,900 ÷ 3,600 = 3.306.
- Take the square root: √3.306 = 1.82 m².
The same patient by the other formulas: Du Bois 1.81, Haycock 1.83, Gehan-George 1.83, Boyd 1.84 m². A 183 cm, 91 kg adult comes out at 2.15 m² by Mosteller and 2.13 by Du Bois. In pounds and inches, 5 ft 7 in (67 in) and 154 lb gives about 1.82 m² with Mosteller.
BSA calculator in cm/kg and in/lb: how to use it
Pick the units you measure in, type height and weight, and choose a formula. The result updates as you type, shows the arithmetic with your numbers, and lists every formula in one table so you can document which one you used.
The address bar keeps your inputs, so you can send a calculation to a colleague. Nothing leaves your browser. Print or save as PDF if the number goes into a chart note.
For aesthetic and surgical practices
BSA shows up in practices as a size-indexed number in a protocol or a record, and in published scales that use it. If a protocol of yours says to index a measurement to BSA, this gives you the figure with the formula named. It does not choose any dose or treatment.
Keep the height, weight and the formula you used with the visit record. Prospyr's charting holds them with the rest of the chart. Related calculators: ideal body weight and estimated blood volume.
Frequently asked questions
What is the Mosteller formula for BSA?
The Mosteller formula is BSA (m²) = √(height in cm × weight in kg ÷ 3,600). It was published in the New England Journal of Medicine in 1987 as a simplified calculation. For 170 cm and 70 kg it gives 1.82 m². You can run it with a pocket calculator that has a square root key, which is much of why it is popular.
How do you calculate BSA in pounds and inches?
Convert first, then use the metric formula: multiply inches by 2.54 for centimeters and pounds by 0.4536 for kilograms. This calculator does that for you when you switch the units toggle. Mosteller can also be written directly in inches and pounds as BSA = √(height in × weight lb ÷ 3,131).
Which BSA formula is best: Mosteller, Du Bois or Haycock?
For typical adult heights and weights the formulas agree within about 1 to 2 percent, as the side-by-side table shows. The differences grow at the extremes, such as very small children or very high weights. The right formula is whichever one your protocol, order set or reference says to use, so use the one named there.
What is a normal body surface area?
Body surface area is not a pass-or-fail number, so there is no normal range to meet. It simply scales with body size: the adult examples on this page run from about 1.8 to 2.2 m², and children are smaller. This tool reports a calculated number, not a judgment about the person.
Is the Mosteller BSA formula accurate for children and obese patients?
Mosteller, Du Bois and the others are estimates fitted to particular groups, and none is exact for every body type. Haycock was validated in infants, children and adults according to its title, and Verbraecken and colleagues compared several formulas in normal-weight, overweight and obese adults. Treat the output as an estimate.
Does this calculator tell me a dose?
No. It only does the arithmetic from height and weight to square meters. Any use of BSA in a dose, an index or a protocol is decided by the treating provider and the product label, not by this page.
Sources and scope
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098. PMID 3657876
Original publication of the square-root formula.
- Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. J Pediatr. 1978;93(1):62-66. PMID 650346
Original publication of the Haycock formula.
- Verbraecken J, et al. Body surface area in normal-weight, overweight, and obese adults. A comparison study. Metabolism. 2006;55(4):515-524. PMID 16546483
Peer-reviewed comparison of published BSA formulas, including Du Bois, Gehan-George and Boyd. The Du Bois (1916), Gehan-George (1970) and Boyd (1935) constants used here are the ones in common published use.
A math aid, not medical advice. BSA is an estimate; confirm the formula your protocol or product label specifies. Dosing and treatment decisions belong to the treating provider.