Body Surface Area Calculator
Estimate your total skin surface area from height and weight, a clinical reference number.
Fill in the form and your result lands here.
Learn the details
This tool uses two validated formulas: Du Bois (BSA = 0.007184 × height^0.725 × weight^0.425) and Mosteller (BSA = √(height × weight / 3600)). BSA is commonly used in medical dosing and metabolic assessments.
Body surface area is one of the few numbers on this site that I will openly tell you is probably not for you. It is a clinical reference figure with a narrow job, and it is here mostly so that when a doctor or a protocol mentions it, you can see where the number comes from.
What the number represents
BSA is an estimate of the total external area of your skin, reported in square meters. Nobody measures it directly outside of research settings, because doing it properly meant wrapping cadavers in paper and measuring the paper, which is genuinely how the early work was done. Instead it gets predicted from two things clinicians already have on the chart, your height and your weight. An average adult lands somewhere around 1.7 square meters. Because the inputs are just height and weight, BSA is a size scaler rather than a health measure, and it says nothing about your body composition or your fitness.
A worked example
Take someone 5 foot 10 and 180 pounds. The tool converts that to 177.8 centimeters and 81.6 kilograms before doing anything else, since both formulas are metric. Mosteller multiplies height by weight, giving 14,517, divides by 3,600 to get 4.0324, then takes the square root, which lands at 2.01 square meters. Du Bois runs a different set of exponents on the same two inputs and returns 2.00. Those two answers differ by about half a percent, which is typical for people near the middle of the height and weight distribution.
Why two formulas
Du Bois and Du Bois published theirs in 1916 from a sample of nine people, which is a small foundation for a formula that is still in use today. Mosteller published a much simpler version in 1987 that is easy enough to do on paper, and it agrees closely with Du Bois through most of the normal range. They drift apart at the edges. Run the same math for someone 6 foot 4 and 250 pounds and Du Bois returns 2.44 while Mosteller returns 2.47. I show both rather than picking one, because a gap between two respected formulas is itself useful information about how precise any single estimate really is.
What it is genuinely used for
The real uses are clinical. Chemotherapy dosing is the best known one, where drug amounts are prescribed per square meter of BSA rather than per kilogram of bodyweight. Cardiac index takes the volume of blood the heart pumps per minute and divides it by BSA so hearts of different sized people can be compared fairly. Kidney function estimates get normalized to 1.73 square meters for the same reason. Burn assessment and some pediatric fluid calculations use it too. The common thread is scaling a physiological quantity to body size so that two different people can be put on the same axis.
What to do with it in the gym
Honestly, very little. There is no training or nutrition decision I would make differently based on your BSA, and I would not track it month to month. If you came here because a provider referenced the number, calculate it, note it, and take the question back to them, since dosing decisions belong with the person prescribing. If you were browsing and want something that actually changes what you do this week, your daily calorie needs and your protein target are far better places to spend the attention. This tool is a reference, and I would rather say that plainly than dress it up as something it is not.
Sources: Du Bois and Mosteller BSA formulas
Both formulas produce similar results; Mosteller is simpler by hand. General fitness rarely needs BSA unless a medical provider or protocol references it.