Quick answerA body surface area calculator estimates external body area from height and weight. It reports common formulas such as Mosteller and Du Bois, which can produce slightly different values for the same person.
What body surface area means
Body surface area, usually expressed in square meters, is an estimate used in parts of medicine and physiology. Height and weight are combined because neither measurement alone describes overall body size well enough for this purpose.
BSA is not the same as body mass index. BMI relates weight to height squared and is used as a screening measure, while BSA estimates external area. A person can have the same BMI as another person but a different BSA because their absolute height and weight differ.
Mosteller and Du Bois formulas
The Mosteller formula takes the square root of height in centimeters multiplied by weight in kilograms and divided by 3,600. It is popular because the arithmetic is simple. The Du Bois formula uses height and weight raised to fitted powers from an older empirical model.
Differences between formulas are usually modest for typical adult measurements but can be more noticeable at body-size extremes. Clinical protocols may name a required formula, and that named method should be used consistently.
How to use this body surface area calculator
- Choose metric or US customary units.
- Enter measured body weight and height.
- Compare the Mosteller result with four other formulas; small differences are expected.
Formula and method
BSA formulas estimate rather than directly measure surface area. Results can be less reliable at body-size extremes.
BSA calculation example
For a person who is 170 centimeters tall and weighs 70 kilograms, the Mosteller calculation is the square root of (170 × 70 ÷ 3,600). The estimated BSA is about 1.82 square meters.
The Du Bois result is close but not identical because it uses different exponents. When a dose or clinical decision depends on BSA, use the formula and rounding method specified by the clinician or protocol.
Common mistakes to avoid
- Entering pounds as kilograms or inches as centimeters.
- Assuming BSA and BMI measure the same thing.
- Switching formulas in the middle of a clinical series.
- Using an online estimate to choose or change medication without a clinician.
Accuracy and practical limits
BSA formulas estimate population-level relationships rather than directly measuring skin area. The calculator converts units before applying published equations, but it cannot assess whether a formula is appropriate for a child, pregnancy, edema, obesity, or a specific treatment protocol.
Primary references: Formula references: Mosteller (1987) and Du Bois & Du Bois (1916).
Frequently asked questions
Which BSA formula should I use?
Use the formula specified by the clinical protocol or professional who requested the value. Mosteller is common because it is simple.
Why do formulas disagree?
They were developed from different samples and mathematical fits.
Can I use this to calculate a medication dose?
Only follow a qualified clinician's explicit formula and instructions. Do not self-dose from a web result.