Body surface area is the total external area of the body, expressed in square metres. Nobody measures it directly outside a laboratory, so it is estimated from height and weight using regression equations fitted to cadaver and photographic studies. Du Bois and Du Bois published the first widely used version in 1916 from just nine subjects, and it is still the reference against which newer equations are compared.
Surface area matters because several physiological quantities scale with it far better than with weight alone. Metabolic rate, cardiac output and glomerular filtration are all conventionally normalised per square metre, which lets a small adult and a large one be compared on the same footing. Mosteller simplified the arithmetic in 1987 to a single square root, and Haycock refitted the exponents on a sample that included children.
For an adult of 175 cm and 70 kg Du Bois returns 1.848 m², Mosteller 1.845 m² and Haycock 1.847 m². The three agree to within 0.003 m² here, which is typical for mid-range adults; they diverge more at the extremes of size, where the original samples had few subjects.
The formula
BSA- Body surface area in square metres
Du Bois- Du Bois & Du Bois 1916, the reference equation
Mosteller- √(kg × cm ÷ 3600), published 1987
Haycock- 0.024265 × cm^0.3964 × kg^0.5378, fitted including children
How it works, step by step
- Enter your height in centimetres.
- Enter your weight in kilograms.
- The gauge shows the Du Bois estimate in square metres.
- Mosteller and Haycock estimates appear below for comparison.
Worked examples
175 cm and 70 kg
Du Bois raises 175 to the power 0.725 and 70 to the power 0.425, multiplies them and scales by 0.007184, giving 1.8481 m². Mosteller takes the square root of 70 × 175 ÷ 3600 = 3.4028, which is 1.8447 m².
Where the methods part company
At 190 cm and 110 kg Du Bois gives 2.377 m² and Mosteller 2.409 m², a gap of 0.032 m². At 150 cm and 45 kg the gap narrows to 0.000 m².
How to read your score
Frequently asked questions
Which equation should I use?
Mosteller is the most common in practice because it is easy to check by hand and performs as well as the longer equations across most of the adult range. Du Bois remains the historical reference, and Haycock is preferred where children are involved.
Why is surface area used instead of weight?
Because heat loss, cardiac output and renal filtration all track surface area more closely than mass. Normalising per square metre makes measurements comparable between people of very different size.
What is a typical adult BSA?
Most adults fall between about 1.6 and 2.0 m². The 175 cm, 70 kg example here gives 1.85 m², and adult averages are often quoted as roughly 1.9 m² for men and 1.6 m² for women.
Why do the three answers differ?
Each was fitted to a different sample with different exponents. Du Bois used nine subjects, Haycock included children, and Mosteller was designed as a simplification. Small differences in exponent compound at the extremes of height and weight.
Can I use this for medication dosing?
No. Dose calculations are a clinical task with checks that this page does not perform. It is an estimate derived from a population equation, not a diagnosis, and it is not a substitute for assessment by a qualified clinician who can see your full history and examine you.
Body surface area reference
| Height and weight | Du Bois (m²) | Mosteller (m²) | Difference (m²) |
|---|---|---|---|
| 150 cm, 45 kg | 1.370 | 1.369 | +0.000 |
| 160 cm, 55 kg | 1.563 | 1.563 | -0.000 |
| 170 cm, 65 kg | 1.754 | 1.752 | +0.002 |
| 175 cm, 70 kg | 1.848 | 1.845 | +0.003 |
| 180 cm, 80 kg | 1.996 | 2.000 | -0.004 |
| 185 cm, 90 kg | 2.141 | 2.151 | -0.010 |
| 190 cm, 110 kg | 2.377 | 2.409 | -0.032 |
Both columns computed from the published equations; the sign shows which runs higher.