What this calculator does
Body surface area is the total external area of the body, in square metres. It matters clinically because many physiological quantities, cardiac output, glomerular filtration, and the dosing of several drug classes, scale better with surface area than with body weight alone.
Three formulas are shown. Du Bois, published in 1916, is the long-standing reference. Mosteller, from 1987, is far simpler and gives results close enough that it has become the more common choice in practice. Haycock is included as a third comparison; the three typically agree within a few per cent.
The formula
Each formula is a regression fitted to measured surface areas, using height and weight as predictors. Du Bois raises each to a fractional power; Mosteller simplifies this to a single square root, which is why it can be done mentally and still lands close to the reference.
| Term | Meaning |
|---|---|
| BSA | Body surface area, in square metres. |
| Du Bois | 0.007184 × height^0.725 × weight^0.425. |
| Mosteller | The square root of height × weight ÷ 3600. |
| Haycock | A 1978 formula, originally developed with paediatric data. |
The inputs explained
| Field | What to enter |
|---|---|
| Height (cm) | Height in centimetres. |
| Weight (kg) | Body weight in kilograms. |
When to use it
Clinical drug dosing
Several drug classes, chemotherapy agents most notably, are dosed per square metre of surface area rather than per kilogram. Which formula a protocol specifies matters, since the results differ slightly.
Calculating cardiac index
Cardiac output divided by body surface area gives cardiac index, which allows comparison between patients of very different sizes.
Comparing the formulas
Run the same measurements through all three. They usually agree closely for average adults and diverge more at the extremes of height and weight, which is where the choice of formula starts to matter.
Assessing burns and fluid requirements
Burn assessment expresses injury as a percentage of total body surface area, and fluid resuscitation protocols are calculated from it.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Body surface area at different weights
A person of 175 cm at a range of body weights, through all three formulas.
| Weight | BSA (Du Bois) | BSA (Mosteller) | Haycock |
|---|---|---|---|
| 50 kg | 1.60 m² | 1.56 m² | 1.54 m² |
| 60 kg | 1.73 m² | 1.71 m² | 1.70 m² |
| 75 kg | 1.90 m² | 1.91 m² | 1.92 m² |
| 90 kg | 2.06 m² | 2.09 m² | 2.11 m² |
| 105 kg | 2.20 m² | 2.26 m² | 2.30 m² |
| 120 kg | 2.32 m² | 2.42 m² | 2.47 m² |
How height changes the result
A fixed 75 kg across a range of heights.
| Height | BSA (Du Bois) | BSA (Mosteller) | Haycock |
|---|---|---|---|
| 150 cm | 1.70 m² | 1.77 m² | 1.80 m² |
| 160 cm | 1.78 m² | 1.83 m² | 1.85 m² |
| 170 cm | 1.86 m² | 1.88 m² | 1.89 m² |
| 180 cm | 1.94 m² | 1.94 m² | 1.94 m² |
| 190 cm | 2.02 m² | 1.99 m² | 1.98 m² |
| 200 cm | 2.10 m² | 2.04 m² | 2.02 m² |
Questions
What is an average body surface area?
Roughly 1.7 m² for an average adult: commonly cited as about 1.9 m² for men and 1.6 m² for women. Children are considerably lower, which is why paediatric dosing uses it so heavily.
Which formula should I use?
Follow whatever your protocol specifies, since the results differ slightly and consistency matters more than choosing a theoretical best. Mosteller is the most widely used in practice because of its simplicity; Du Bois remains the classical reference.
Why dose drugs by surface area rather than weight?
Because several physiological processes, metabolic rate, renal clearance, blood volume, scale more closely with surface area than with mass. For drugs with a narrow therapeutic window, that difference is clinically significant.
Is body surface area used outside medicine?
Occasionally, in physiology and thermal modelling, since heat exchange with the environment happens across the skin. But its main use is clinical.
Does this replace clinical judgement?
No. This is a calculation tool. Any dosing decision belongs with the treating clinician, who will apply the protocol, the patient’s condition and the relevant guidelines.
For other body composition measures, see BMI and body fat percentage.