What body surface area is
Body surface area, or BSA, is an estimate of the total skin area of a person, written in square meters (m²). Nobody measures it directly in everyday life. Instead, a formula turns two easy measurements, height and weight, into one number. Because skin area grows with body size but not in a straight line with weight, the formulas use square roots or fractional powers rather than simple multiplication.
BSA is used in some areas of medicine and physiology to scale a quantity to body size, for example when a published protocol expresses a value per square meter. This page does not do any of that. It is a calculator and a comparison of formulas for adults, and it does not provide a dose, a treatment or a recommendation. Anything that depends on a BSA value in care should be calculated and checked by the clinician or pharmacist responsible, using the method their protocol names.
The four formulas on this page
The calculator evaluates four published equations on the same height H in centimeters and weight W in kilograms. Each returns square meters.
- Mosteller (1987): BSA = √(H × W ÷ 3600). It is the simplest to compute by hand and the default here.
- Du Bois and Du Bois (1916): BSA = 0.007184 × W0.425 × H0.725. The oldest of the four.
- Haycock (1978): BSA = 0.024265 × W0.5378 × H0.3964. Another fitted equation with different exponents.
- Gehan and George (1970): BSA = 0.0235 × W0.51456 × H0.42246. The fourth fitted equation, again with its own exponents.
The Mosteller equation was published as a deliberately simple alternative to the older, more complicated ones (Mosteller RD, New England Journal of Medicine, 1987;317:1098). A formula reference for all four is maintained in the US Department of Veterans Affairs clinical reminders documentation.
Worked example: 175 cm and 70 kg
Take an adult who is 175 cm tall and weighs 70 kg. With Mosteller, H × W = 175 × 70 = 12,250, divided by 3,600 is 3.4028, and the square root is 1.845 m². The other three formulas give 1.848 m² (Du Bois), 1.847 m² (Haycock) and 1.854 m² (Gehan–George).
The largest and smallest of the four differ by 0.009 m², which is 0.5% of the Mosteller value. For an ordinary adult, the choice of formula changes the third decimal place, not the first. That is why the calculator shows three decimals: two decimals would hide the differences completely.
How the formulas differ at other sizes
Because the equations use different exponents, the gaps between them change with body size. At 160 cm and 55 kg, the four values span 0.013 m² (0.9% of Mosteller): Mosteller 1.563, Du Bois 1.563, Haycock 1.566, Gehan–George 1.577. At 190 cm and 95 kg they span 0.015 m² (0.7%): Mosteller 2.239, Du Bois 2.234, Haycock 2.249, Gehan–George 2.246.
No one of them is the true value, because the true value is a skin area that none of these equations measures. They are statistical fits. If a protocol, a textbook or a hospital policy names one equation, use that one; the comparison here is for understanding how much the choice matters, not for picking a winner.
How to read the chart and the table
The first chart draws each result as a bar that starts at zero. Because the four values are so close, the bars look almost the same, and that is the honest picture: the formulas agree to within a few percent. The second strip zooms the axis in so that you can see the order of the values and the size of the gaps. Its axis does not start at zero, and the page says so under it. The results table lists every value with its difference from Mosteller in square meters and in percent, so the chart is never the only place a number appears.
Using metric or US units
You can enter height in centimeters or in feet and inches, and weight in kilograms or pounds. US values are converted with 1 inch = 2.54 cm and 1 pound = 0.45359237 kg before any formula runs. When you switch units the page keeps the exact underlying value rather than the rounded text on screen, so switching back and forth does not slowly change your result. The accepted input bounds are 100 to 250 cm and 25 to 350 kg, and the inch box must be 0 up to but not including 12. These are limits of this calculator, not clinical limits.
Limits you should know about
- It is an estimate. Two people with the same height and weight can have slightly different skin areas.
- Adults only. This page has no pediatric mode and does not provide values for infants or children, who are usually assessed with different methods and clinical references.
- No dosing. The page never turns a BSA into a medicine dose or an amount of any substance.
- Extremes. Very high or very low body weight is where the formulas disagree most and where published guidance often asks for clinical judgment.
- Body composition. BSA ignores how much of your weight is muscle or fat. For that, see the body fat calculator, and for the weight-to-height ratio, the BMI calculator.
More tools for body measurements, energy and training are on the Fitness & Health calculators page.
Frequently asked questions
Which BSA formula is the most accurate?
None of them is the reference, since skin area is not what any of them measures. They are curve fits that agree to within a few percent for ordinary adult sizes. Use the formula your protocol or institution names. Mosteller is the default here because it is simple and easy to check by hand.
Why does this calculator show three decimals?
The four formulas differ in the third decimal place for a typical adult. Rounding to two decimals would make several of them look identical and hide the comparison.
Can I use this for a child?
No. This page is for adults and enforces adult input bounds. Children are assessed with other methods, so ask the clinical team for the right reference.
Does BSA tell me my ideal weight or body fat?
No. It is only a size measure. Weight status is usually discussed with BMI and body composition tools, and neither replaces a clinician's assessment.
Is the result a medicine dose?
No. This calculator never produces a dose. If a treatment is expressed per square meter, the calculation must be done and double-checked by the responsible clinician or pharmacist.
Sources
Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317(17):1098 (PubMed). Formula comparison reference: US Department of Veterans Affairs, Clinical Reminders documentation. This page is educational information and not medical advice.