Body surface area (BSA) by the Mosteller formula is the square root of height in cm times weight in kg, divided by 3600. A person who weighs 70 kg and is 175 cm tall has a BSA of 1.845 m². The Du Bois formula gives 1.848 m² for the same person. This calculator uses Mosteller.
How the formula works
Multiply weight in kilograms by height in centimeters. Divide by 3600. Take the positive square root. The result is Mosteller BSA in square meters. For a BMI from the same two inputs, see the BMI calculator.
BSA formulas compared
Weight in kg (W), height in cm (H). Results in m².
| Formula | Equation | 70 kg, 175 cm |
|---|---|---|
| Mosteller (this calculator) | √(H × W ÷ 3600) | 1.845 |
| Du Bois | 0.007184 × H0.725 × W0.425 | 1.848 |
| Haycock | 0.024265 × H0.3964 × W0.5378 | 1.847 |
Du Bois may overestimate BSA in people with obesity, and Haycock was developed with children in mind (source: StatPearls, Body Surface Area).
BSA examples (Mosteller)
| Weight | Height | BSA (m²) |
|---|---|---|
| 55 kg | 160 cm | 1.563 |
| 60 kg | 165 cm | 1.658 |
| 70 kg | 170 cm | 1.818 |
| 70 kg | 175 cm | 1.845 |
| 80 kg | 180 cm | 2.000 |
| 90 kg | 170 cm | 2.062 |
| 100 kg | 185 cm | 2.267 |
Worked example
70 × 175 = 12250. Divide by 3600 to get about 3.40278. Square root yields about 1.8447, reported here as about 1.845 m².
| Input | Value |
|---|---|
| Weight | 70 kg |
| Height | 175 cm |
| (w × h) / 3600 | about 3.40278 |
| BSA (Mosteller) | about 1.845 m² |
- Pounds and feet: 154 lb × 0.45359237 = 69.853 kg (use the weight converter). 5 ft 9 in = 69 in × 2.54 = 175.26 cm (or use the height converter). √(69.853 × 175.26 ÷ 3600) = 1.844 m². Factors from NIST SP 811 App. B.9.
- Doubling weight multiplies BSA by √2 (1.414), not by 2. At 175 cm, 70 kg gives 1.845 m², and each 5 kg adds about 0.06 m²: 75 kg gives 1.909 and 80 kg gives 1.972.
How to use the fields
- Weight (kg) is body mass in kilograms.
- Height (cm) is stature in centimeters.
Unit conversion before you start
If height is 5 ft 9 in, convert to centimeters first. If weight is in pounds, convert to kilograms. Mixing imperial inputs into kg and cm fields will distort BSA badly.
Write the converted values in your notes so a reviewer can see the unit path, not only the final square meters.
Common mistakes
- Entering height in meters (1.75) instead of centimeters (175)
- Leaving weight in pounds while the field expects kilograms
- Forgetting the divide by 3600 step in hand work
- Treating BSA as a diagnosis rather than a geometric estimate
Educational context only
Some clinical worksheets reference BSA. This calculator does not select drugs, doses, or care plans. It only evaluates Mosteller from the two anthropometric inputs. To estimate kidney filtration from a creatinine result, use the eGFR calculator.
When you cite a BSA number in homework, name Mosteller explicitly so readers know which formula produced it.
Measurement quality
Morning weight, clothing, and stadiometer technique all move inputs. Tape height carefully and use a consistent weighing routine when you compare BSA across dates.
Rounding height to the nearest centimeter is usually enough for example work. Unrealistic precision in the inputs does not create clinical certainty in the output.
Limitations
Mosteller is an estimate from two measurements. It does not image the body, adjust for amputation, or replace clinical protocols. Mosteller underestimated measured BSA by about 4% in one study of children (PubMed 22211780). Educational use only.