Last updated: 2026-06-21

Body Surface Area (BSA)

Body surface area (BSA) is an estimate of the total external area of the human body, expressed in square metres. Because it scales with overall body size more faithfully than weight alone, clinicians use it to standardise physiological measurements and to size doses of weight-and-height-dependent medications. This calculator computes BSA from height and weight using three established formulas — Mosteller, Du Bois, and Haycock.

Why body surface area is used

Many physiological quantities track body size rather than weight. Cardiac output, for example, is routinely divided by BSA to give the cardiac index, allowing a small adult and a large adult to be compared on the same scale. Glomerular filtration rate is similarly normalised to a reference surface area of 1.73 m². The most common everyday use is in pharmacology: many drugs, and chemotherapy agents in particular, are prescribed in milligrams per square metre so that the dose reflects the patient's size. Typical adult values fall near 1.7 m² for women and 1.9 m² for men.

The formulas

The Mosteller formula, introduced in 1987, is the simplest and the most widely used today:

$\mathrm{BSA} = \sqrt{\dfrac{h \cdot w}{3600}}$

where $h$ is height in centimetres and $w$ is weight in kilograms. The constant 3600 makes the result come out in square metres.

The older Du Bois and Du Bois formula (1916) remains the historical reference:

$\mathrm{BSA} = 0.007184 \cdot h^{0.725} \cdot w^{0.425}$

The Haycock formula (1978) was fitted on a sample that included infants and children, which makes it a common choice in paediatrics:

$\mathrm{BSA} = 0.024265 \cdot h^{0.3964} \cdot w^{0.5378}$

All three are empirical fits to measured surface areas, which is why the exponents are not round numbers — they were chosen to reproduce observed data across a range of body sizes.

Worked example

The Du Bois and Haycock formulas give 1.81 m² and 1.83 m² for the same person — a spread of about one percent, which is typical for adults in the normal range. The agreement narrows for average builds and widens at the extremes of height and weight.

Limitations

These equations are population estimates derived from relatively small samples, so an individual's true surface area can differ from the calculated value. They also do not capture body composition: two people with the same height and weight return the same BSA regardless of how much is muscle or fat. Dosing and other clinical decisions should always be made by a qualified professional using validated protocols rather than a calculated number alone.

If you are comparing body-size metrics, the BMI Calculator screens weight relative to height, while the BMR Calculator estimates daily resting energy expenditure.