Body Surface Area Calculator — Mosteller & Du Bois

How it works

BSA scales with both height and weight, which is why medicine often doses by it rather than by weight alone — two people of the same weight but different heights have different surface areas and different metabolic sizes. The Mosteller formula (1987) reduced the calculation to a single square root, which is why it became the clinical default; the Du Bois formula (1916) is the original and uses fractional powers of height and weight. For typical adults the two agree to within a percent or two, shown side by side in the comparison. Both take height in centimetres and weight in kilograms internally, whatever units you enter.

Worked example

For a person 170 cm tall weighing 70 kg, Mosteller gives BSA = √(170 × 70 ÷ 3600) = √3.306 ≈ 1.82 m². Du Bois gives 0.007184 × 70^0.425 × 170^0.725 ≈ 1.81 m² — a difference of under 1%. A larger person at 185 cm and 95 kg comes out around 2.21 m² by Mosteller (2.19 m² by Du Bois): BSA grows with size but slowly, because both terms are raised to powers below one.

Frequently asked questions

What is body surface area used for?

Chiefly in medicine: dosing chemotherapy and some other drugs (many are prescribed per m² of BSA), indexing cardiac output (cardiac index = output ÷ BSA), estimating fluid needs, and assessing the extent of burns. It captures body size in a way that correlates with metabolic rate and organ function better than weight alone.

Mosteller or Du Bois — which is better?

Mosteller is the usual clinical choice because it's simple and accurate enough; Du Bois is the historical original and still widely referenced. They rarely differ by more than a couple of percent for adults, so the choice mostly matters for consistency within a given setting. This page shows both; the primary figure uses Mosteller.

Why does BSA use a square root?

The Mosteller formula is a simplification: surface area scales roughly with the square root of the product of height and weight, and dividing by 3600 puts the answer in square metres when height is in cm and weight in kg. It's an empirical fit to measured data, not a geometric derivation — the body isn't a simple shape.

Is a "normal" BSA a thing?

There's no health category for BSA the way there is for BMI — it's a size measurement, not a risk classification. Average adult BSA is roughly 1.7 m² for women and 1.9 m² for men, but "normal" only means typical for your height and weight. A higher or lower BSA isn't good or bad on its own.

Does BSA work for children?

The same formulas are used for children and are common in paediatric drug dosing, but paediatric dosing has its own rules and safety limits. This calculator gives the BSA value; it does not compute doses. For any dosing decision, use the clinical protocol and a professional, not a general estimate.

Why might my result differ from another calculator?

Different tools use different BSA formulas — beyond Mosteller and Du Bois there are Haycock, Gehan-George, and Boyd equations, each fitted to different data. They cluster closely but not identically. If you need a specific one (for example, a hospital's standard), match the formula, not just the calculator.

How accurate is this, and what does it exclude?

The formulas are exact for the height and weight entered, but they're estimates of a real surface that was never measured on you — expect a few percent of uncertainty. They don't account for body shape, amputations, or unusual proportions, and they are not a substitute for clinical dosing calculations, which follow protocol-specific rules.