Financial term · Reviewed August 17, 2026
Body surface area
Body surface area: The total external surface area of the body, estimated from height and weight. Some clinical dosing and burn assessment work from it. The Body Surface Area Calculator returns this figure from mosteller: BSA = √(height(cm) × weight(kg) ÷ 3600). At that calculator’s documented worked-example inputs the body surface area (mosteller) is 1.9; holding every other input steady, moving weight from 136 to 204 moves it from 1.7 to 2.1, a spread of 0.389.
Some clinical dosing scales to surface area instead of weight. So the estimate matters precisely where being wrong is expensive. Two people at the same weight can differ in surface area if their heights differ, and the dosing follows the surface area.
| Term | Body surface area |
|---|---|
| Category | Body Composition |
| How it is found | Mosteller: BSA = √(height(cm) × weight(kg) ÷ 3600) |
| Worked example | Body surface area (Mosteller): 1.9 |
| Computed by | Body Surface Area Calculator |
| Related terms | 6 defined in this glossary |
Before you rely on it
What to check
Which formula produced it matters, because the common estimating equations disagree at the extremes of height and weight.
The common error
Where people go wrong with body surface area
Using an estimate for anything self-directed. This is reference information for a conversation with a clinician, and nothing here is a basis for dosing anything.
Worked through
Body surface area in plain numbers
The Mosteller formula estimates body surface area as the square root of height in centimeters times weight in kilograms, divided by 3,600. For someone 170 cm tall and 70 kg, that is the square root of 11,900 ÷ 3,600, which is the square root of 3.306, or 1.82 square meters; a 190 cm, 95 kg person comes out near 2.24, and a child of 110 cm and 20 kg is about 0.78. The values are handy because surface area scales more smoothly with body size than weight does, which is why some clinical calculations use it.
Easily confused
Body surface area and its neighbours
BSA is not BMI, although both use height and weight. BMI is a ratio for screening weight status. BSA estimates the area of the skin. Several formulas exist, including Mosteller, DuBois and Haycock, and they give slightly different answers, especially at extremes of size. Lean body mass is again different: it excludes fat. Choosing which formula to use matters when the result feeds a dose calculation, and clinicians follow the one set out in their protocol, not whichever a tool defaults to.
In real decisions
Where body surface area turns up
Clinicians use BSA to scale certain drug doses, most notably in cancer chemotherapy, and to index measurements such as cardiac output and kidney function to body size. Physiologists use it in research. Burn assessment relies on percentages of body surface. Outside medicine it is rarely needed; a person using a calculator for curiosity should not use the result to work out a medication dose. Dosing decisions belong to the prescriber, who accounts for many factors beyond a single number.
Know the edges
Where body surface area stops being reliable
Formulas estimate the area from population data and can be off for people who are very large, very small or unusually proportioned. They do not account for body composition. Small measurement errors in height or weight carry through to the result. Differences among formulas are usually small for typical adults and larger at extremes. This page explains a calculation for education. It is not medical advice, and any clinical use needs a professional's judgment.
Quick answers
What people ask about body surface area
Why is body surface area used for doses? Some processes, such as heat loss and organ size, scale with surface area more closely than with weight. That is why certain treatments are dosed per square meter. The prescriber, not a calculator, decides the dose.
Which formula is best? Several are in use, and for typical adults they agree within a few percent. Mosteller is popular for its simplicity. Clinical protocols specify which formula to use.
Put it to work
How body surface area is calculated
At the body surface area calculator’s worked-example inputs, body surface area (mosteller) is 1.9, body surface area (du bois, cross-check) is 1.9. Moving weight from 136 to 204 moves that first figure from 1.7 to 2.1.
Open the Body Surface Area Calculator →
These are population-based formulas, not diagnoses. Frame size, muscle mass, ethnicity and other factors these formulas do not measure can shift what is healthy for a given person. Consult a healthcare provider for individual guidance.
Related vocabulary
Terms used alongside this one
Keep reading
Nearby in the glossary
- ← Body mass index
- Bond coupon →
- All 174 defined termsThe complete Free Calculators Online financial glossary.