Body Surface Area Calculator (Mosteller, DuBois, Haycock, Boyd)

Understanding the body surface area calculator — concept and principle

Body surface area (BSA) is the estimated total area of the skin, in square metres (m²). It is used mainly in medicine: many chemotherapy doses are prescribed per m², cardiac output is indexed to BSA, and kidney function (eGFR) is reported per 1.73 m², a long-used typical adult value. BSA cannot be measured directly in daily practice, so it is estimated from height and weight. This calculator shows four well-known formulas side by side.

Spread flat, the skin of a 175 cm, 75 kg adult covers about 1.91 m²; the four formulas differ by only 0.02.

How it is calculated

Weight W is in kilograms and height H in centimetres; every result is in m².

Mosteller (1987): BSA = √(H × W ÷ 3600)
DuBois (1916): BSA = 0.007184 × W^0.425 × H^0.725
Haycock (1978): BSA = 0.024265 × W^0.5378 × H^0.3964
Boyd (1935): BSA = 0.0003207 × H^0.3 × G^(0.7285 − 0.0188 × log₁₀G), with G = weight in grams

Mosteller is the simplest and widely used in hospitals; DuBois is the classic adult reference; Haycock and Boyd were fitted on data that include children.

The principle

If a body only changed size without changing shape, its surface would grow with length² and its weight with length³. Real builds differ, so researchers measured the skin area of real bodies and fitted power equations of the form a × W^b × H^c. The exponents on weight and height add up to roughly 1, consistent with area being length × length while weight tracks volume. Mosteller showed that the square root of H × W reproduces the DuBois values closely, giving an easy formula.

Worked example

Inputs: weight 75 kg, height 175 cm.
Mosteller: 175 × 75 = 13,125; ÷ 3600 = 3.646; √3.646 = 1.91 m².
DuBois: 0.007184 × 75^0.425 × 175^0.725 = 1.90 m².
Haycock: 0.024265 × 75^0.5378 × 175^0.3964 = 1.92 m².
Boyd: G = 75,000 g, exponent 0.7285 − 0.0188 × 4.875 = 0.637, result 1.92 m².

Each point is the calculator re-run with only “Weight (kg)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Weight (kg)	BSA — Mosteller
18.8	0.95
37.5	1.35
56.2	1.65
75	1.91
93.8	2.13
112	2.34
150	2.7

How to read the result

For an average adult the formulas agree within a few hundredths, as here (1.90–1.92). Typical adult values are around 1.9 m² for men and 1.6–1.7 m² for women. At the extremes, in small children or severe obesity, the formulas diverge more, and clinicians use whichever one their protocol specifies.

Common mistakes

Entering height in metres or inches, or weight in pounds; the constants assume cm and kg.
Switching formulas between visits, which creates artificial changes in a per-m² dose.
Treating BSA as a body-fat or health score; it is only a size estimate.

Keep in mind: BSA is an estimate built on small original samples. Any BSA-based drug dose must be calculated and checked by the prescriber and pharmacist. This is not a diagnosis or a dosing tool.

Frequently asked questions

Which BSA formula is most accurate?

None is best for everyone. Mosteller is the usual default; Haycock is also common in children.

Why is eGFR given per 1.73 m²?

It scales kidney filtration to a standard adult size so people of different sizes can be compared.

Does losing weight change BSA?

Slightly. At 175 cm, going from 75 to 70 kg lowers Mosteller BSA from about 1.91 to 1.84 m².

Sources: Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098 · Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med 1916;17:863–871

Checked 8 Nov 2026. Published formulas cited on the page. For information only — not medical advice.

Your numbers