Body Surface Area (BSA) Calculator

The Mosteller formula, this calculator's default, takes the square root of height in centimeters multiplied by weight in kilograms, divided by 3,600. It was published in 1987 specifically to be simpler to compute by hand than the formulas that came before it, without losing meaningful accuracy.

The DuBois formula predates it by 71 years, originally derived in 1916 from a measured sample of just 9 people. Despite that small original study, it remains the formula many clinical references still treat as the default standard, and it's built differently: height and weight are each raised to their own fractional exponent and multiplied together with a fixed constant.

Does BSA Work the Same Way for Children?

Yes. Both the Mosteller and DuBois formulas are used for pediatric patients the same way as for adults, using the child's own height and weight. Some clinical references prefer a third formula, Haycock, specifically for infants and young children, though the difference between Haycock and Mosteller is generally small for most pediatric body sizes.

For context, here are commonly cited average BSA values by age group:

These are population averages, not targets, and an individual's real BSA can differ meaningfully based on their own actual height and weight. A BSA of 1.73 m² specifically shows up often as a reference value, since it's the estimated glomerular filtration rate's own standard reference body size, used to make eGFR results comparable across people of different sizes.

Every BSA formula was statistically fit to a different measured group of people, at a different time, so small disagreement between them is expected, not a sign either one is wrong. For a typical adult body size, Mosteller and DuBois usually land within well under 1% of each other.

The gap grows at less typical body sizes, and real-world validation studies paint a more significant picture than either formula's own history suggests. A 2022 clinical review comparing calculated BSA against direct tape measurements of 401 people found that DuBois overestimates true BSA by more than 15%, especially in patients who are obese, and that Mosteller runs even higher still, roughly 3 to 5 percent above DuBois on the same person. For someone at an unusual height or weight, a gap of that size can translate into a real difference in a calculated medication dose, which is part of why BSA-based dosing for medications with a narrow safety margin, and BSA-indexed clinical measurements like aortic valve area, remain a genuine area of active clinical discussion rather than a fully settled question.

Many drugs, especially in oncology, are dosed as an amount per square meter of body surface area rather than a flat dose for everyone. Multiplying that per-m² number by your own BSA gives the actual dose in milligrams: a drug dosed at 100 mg/m² for someone with a BSA of 1.87 m² works out to about 187 mg.

Enter a dose density above if you have one, and the calculator will show your actual calculated dose alongside your BSA result. This is a reference calculation only. Real dosing also accounts for organ function, prior treatment cycles, and other clinical factors a treating provider reviews, so this figure should never replace an actual prescription or protocol. For medications dosed by weight instead of BSA, see the Drug Dosage Calculator (mg/kg).

Body surface area shows up alongside a few other clinical calculations:

• IV Drip Rate Calculator: another quick bedside calculation used alongside dosing decisions in clinical settings.