Body Surface Area Calculator
Body surface area
– m²
Enter a height and a weight.
- Formula
- –
- Spread across all four
- –
All four formulas
| Formula | BSA |
|---|
This works out the arithmetic. The order, the product in your hand and local policy still govern what is given.
How body surface area is calculated
Mosteller: BSA (m²) = √(height in cm × weight in kg ÷ 3600)
Every formula on this page takes the same two measurements and returns square metres. They differ only in the coefficients, which each set of authors fitted to a different population, which is why the numbers they return are close but not equal.
Mosteller is the one most protocols name. It was published in 1987 as a deliberate simplification of the older equations, on the grounds that a formula you can run on a pocket calculator gets used correctly more often than one you cannot.
How much the four formulas disagree
At 170 cm and 70 kg:
| Formula | BSA | Published |
|---|---|---|
| Mosteller | 1.818 m² | Simplified calculation of body-surface area |
| Du Bois & Du Bois | 1.81 m² | A formula to estimate the approximate surface area |
| Haycock | 1.826 m² | Geometric method for measuring body surface area |
| Gehan & George | 1.831 m² | Estimation of human body surface area from height and weight |
The spread is 0.022 m², about 1.2% of the smallest figure. On a drug dosed at 100 mg/m² that is the difference between 181 mg and 183.1 mg, which is why the formula that was used has to travel with the number rather than being assumed.
Where the 1.73 m² figure comes from
1.73 m² is roughly the average body surface area of a young adult, and it is the value eGFR results are normalised to so that kidney function compares across people of different sizes. That normalising step is the reason an eGFR and acreatinine clearance for the same patient are different numbers.
Body surface area also feeds the weight-based dosing calculator wherever a protocol writes a dose in mg/m² rather than mg/kg: the surface area replaces the weight, and everything after that point is the same arithmetic.
Questions about body surface area
- What is the Mosteller formula for BSA?
- Body surface area in square metres is the square root of height in centimetres multiplied by weight in kilograms, divided by 3600. It is the formula most chemotherapy protocols name, largely because it can be done on a basic calculator.
- Which BSA formula should I use?
- Whichever one the protocol or dosing reference you are working from specifies. They are not interchangeable and the difference between them is real, though usually small. Where nothing is specified, Mosteller is the most commonly used.
- What is a normal body surface area?
- Around 1.7 m² for an average adult, which is where the 1.73 m² normalising figure in eGFR reporting comes from. Adult values typically fall between roughly 1.5 and 2.2 m².
- Why is BSA used for dosing instead of weight?
- For some drugs, particularly cytotoxics, body surface area tracks metabolic rate and drug handling more closely than weight alone. It is a convention with known limitations rather than a precise physiological measure, and many protocols cap the value used.