This body surface area calculator works out your body surface area from just your height and weight, and it shows the answer in square metres and square feet. Doctors call this figure BSA for short, and they use it to scale some treatments to body size. Unlike weight alone, surface area reflects both how tall and how heavy you are. This page explains the two classic formulas, walks through a full worked example, and then sets out honestly what the result should and should not be used for.

How the Body Surface Area Calculator Works

First, the Mosteller formula takes the square root of your height in centimetres times your weight in kilograms, divided by 3600. Most clinics use this version, because the maths stays simple and the result matches older methods closely. Next, the Du Bois formula raises your height and weight to small powers and multiplies them by 0.007184. Researchers published that formula in 1916, and it still serves as the historical standard. Finally, this calculator converts both answers into square feet, since 1 square metre equals 10.7639 square feet.

Body Surface Area Calculator Example: 165 cm and 65 kg

Say a woman measures 165 cm tall and weighs 65 kg. First, the Mosteller method multiplies 165 by 65, which gives 10,725. Then it divides 10,725 by 3600, giving 2.979, and the square root of that figure is 1.73 square metres. Next, the Du Bois method works through its powers and gives 1.72 square metres for the same woman. The two methods therefore land within a whisker of each other, which is one reason clinics trust either one. In square feet, her Mosteller result reads about 18.6 square feet.

Typical Body Surface Area Values

For example, a newborn baby starts tiny, at roughly 0.25 square metres. By about ten years of age, a child reaches roughly 1.14 square metres. An average adult woman sits near 1.6 square metres, while an average adult man sits near 1.9 square metres. These published averages give you a rough landmark only, because healthy bodies vary widely at every age and every height.

What Body Surface Area Is Used For, and Its Limits

Clinicians use surface area in several corners of medicine. For instance, some drug doses, including many chemotherapy doses, are scaled to surface area rather than to weight alone. Burn care teams also use it to estimate how much of the body a burn covers and how much fluid a patient needs. However, this body surface area calculator is an educational tool, and its result must never be used to set a dose for anyone. Dosing decisions belong to the treating clinician, who weighs your full medical picture alongside the number. Overall, treat your result as background knowledge that helps you follow the conversation, not as an instruction to act on.

Frequently Asked Questions

Which formula is more accurate, Mosteller or Du Bois?

Both formulas estimate the same thing, and comparison studies find them very close for most adults. Mosteller wins on simplicity, so hospitals use it most often today. Du Bois still appears in older research, which is why this page shows both figures side by side.

Why do doctors use surface area instead of weight alone?

Two adults can share the same weight yet differ greatly in height, and surface area captures both measurements at once. For certain treatments, that combined figure matches how the body handles a drug more closely than weight does. Even so, clinicians adjust every decision to the individual patient in front of them.

Can I use my BSA to work out a medicine dose?

No, never. Dose calculations also depend on the drug itself, on kidney and liver function, and on your overall condition. Only your treating team can set a dose safely. Instead, use this body surface area calculator to understand a figure you may see in your medical notes, and nothing more.

Does body surface area change if I gain or lose weight?

Yes, because weight sits inside both formulas, so a real change in weight moves the result. Height changes matter too, which is why growing children see their surface area climb steadily. After any large change in weight, simply run the numbers again for an up to date figure.

What is a normal body surface area for an adult?

Most adults fall somewhere between about 1.4 and 2.1 square metres, with women averaging near 1.6 and men near 1.9. A figure outside that band is not automatically a problem, because frame size and height play a large part. Your health and how you feel matter far more than matching an average.

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Sources

The simple square root method on this page follows the Mosteller formula, published by R. D. Mosteller in the New England Journal of Medicine in 1987. The second method is the classic Du Bois formula, published by Du Bois and Du Bois in 1916. The typical values quoted on this page are the commonly published averages used in clinical references.