How to use the body surface area calculator
- Choose Metric (cm, kg) or US units (ft, in, lb).
- Enter height and weight. The calculator works for children as well as adults.
- Pick the formula for the main result, or leave it on Mosteller. The table always compares all five.
How body surface area is calculated
Body surface area (BSA) is the area of the outside of the body, in square meters. Measuring it directly is impractical, so formulas estimate it from height (H, in centimeters) and weight (W, in kilograms):
Du Bois and Du Bois published the first widely used formula in 1916, based on careful measurements of just nine people. Boyd (1935) and Gehan and George (1970) refitted it with hundreds of subjects, including children. Haycock (1978) was built for a range from newborns to adults. Mosteller (1987) proposed a simple square-root version that gives almost the same answers as Gehan and George and can be done on any calculator, which is why many hospitals now use it.
Worked example
These are the calculator's defaults: 175 cm and 70 kg.
- Height × weight: 175 × 70 = 12,250
- Divide by 3,600: 12,250 ÷ 3,600 = 3.4028
- Square root: √3.4028 = 1.84 m² (Mosteller), or about 19.9 square feet
The other formulas give 1.85 m² for the same person: Du Bois 1.848, Haycock 1.847, Gehan and George 1.854, and Boyd 1.851. For most adults the five agree within about 2%. The gaps grow for babies and for people with obesity: at 170 cm and 150 kg they span 2.50 to 2.77 m².
What BSA is used for
| Use | Why BSA helps |
|---|---|
| Chemotherapy and some other drugs | Doses are often set per square meter, because BSA tracks blood volume and kidney function better than weight alone |
| Kidney function | eGFR results are reported per 1.73 m², the average adult BSA when the standard was set |
| Heart measurements | Cardiac output is divided by BSA to give the cardiac index |
| Burns | The size of a burn is described as a percentage of the body's surface |
For reference, a newborn has a BSA of about 0.2 m², a 10-year-old about 1.1 m², and most adults fall between about 1.5 and 2.2 m².
Limits
BSA formulas are estimates based on average body shapes. They are less reliable at extremes: very small premature babies, people with severe obesity, and people who have had amputations. Weight changes BSA, so the value should be recalculated after any large weight change. Doctors and pharmacists calculate BSA for treatment themselves, and some cap doses at a set BSA. Never adjust a medicine dose from this page. Ask your care team if you have questions about how your dose was worked out.
Frequently asked questions
Which BSA formula is the best?
There's no single best. Mosteller is the most widely used because it's simple and closely matches the better-tested Gehan and George formula. Du Bois is still common in older research and some labs. Haycock is often used for children. For a typical adult the difference is small.
What is a normal body surface area?
Average adult values are about 1.9 m² for men and 1.6 m² for women, though healthy adults range from roughly 1.5 to 2.2 m². The figure of 1.73 m², used to scale kidney tests, is a historical average for adults.
Why do the formulas give different answers?
Each was fitted to a different group of people and uses height and weight with different exponents. For an average adult they agree within a few hundredths of a square meter. For newborns and for people with severe obesity they can differ by 10% or more.
Can I use BSA to calculate a medicine dose?
No. Dosing involves more than BSA, including kidney function, other medicines and dose limits. Leave it to your doctor or pharmacist, who will use their own validated calculation.
Related calculators
- BMI Calculator — Your body mass index, weight category and healthy weight range, in metric or US units.
- GFR Calculator — Estimate kidney function (eGFR) from a creatinine blood test with the race-free 2021 CKD-EPI equation, and see the GFR category.
- Lean Body Mass Calculator — Lean body mass from your height and weight with the Boer, James and Hume formulas, plus the body fat each implies.
Results are estimates for general information and are not medical advice. Talk to a doctor or other qualified professional about your health. See our disclaimer.