Estimates the surface area of the body from height and weight. Drug doses and fluid volumes often scale with surface area rather than weight, so it is widely used in medicine. Several formulas exist, and the three best known are shown side by side.
Body surface area is the total area of the skin, measured in square metres. An adult typically falls somewhere between 1.6 and 1.8.
Clinically it is used to set drug doses. Cytotoxic chemotherapy in particular is dosed by surface area rather than by weight, because the body's capacity to process a drug, and its exchange of heat and fluid, track surface area more closely than they track mass. It also appears in fluid calculations and in indexing cardiac output to body size.
Surface area cannot be measured directly, so it is estimated from height and weight. Many formulas exist, and this calculator shows the three best known.
The first is the Du Bois formula, published in 1916 and still the most widely used. The second is the Mosteller formula from 1987, which needs only one square root and so is quick enough to do at the bedside. The third is the Fujimoto formula, derived from measurements of Japanese subjects.
Take a height of 170 cm and a weight of 65 kg.
Du Bois gives about 1.7536, Mosteller about 1.7520 and Fujimoto about 1.7072.
Du Bois and Mosteller agree to within a thousandth. Two formulas of completely different shape land in the same place because both are approximations fitted to the same kind of measured data. Fujimoto comes out about 0.05 lower, and that gap is the difference between a formula fitted to Western subjects and one fitted to Japanese subjects.
Which formula to use is usually fixed by local protocol or by the drug itself. A different formula gives a different area, and a different area gives a different dose, so this is not a choice to make on the spot.
These are estimates. At the extremes of build, and in children, the formulas diverge more from each other and from reality. Each was fitted to a modest number of measured subjects, and the further a body sits from that group, the poorer the fit.
This calculator takes height in centimetres and weight in kilograms. Some sources write the same formulas with height in metres, so check the units before comparing against another calculation.