Body Surface Area Calculator

Body surface area (BSA) is the total area of the outer surface of the body, usually given in square meters. It cannot practically be measured on a living person, so it is estimated from height and weight. Doctors use BSA because many physiological quantities, such as metabolic rate, blood volume, kidney filtration and cardiac output, scale more closely with surface area than with weight alone.

The most important clinical use is drug dosing. Many chemotherapy drugs and some other medicines with a narrow margin between an effective and a toxic dose are prescribed in milligrams per square meter. BSA is also used to index cardiac output (the cardiac index), to set doses of corticosteroids and to judge the extent of burns relative to total skin area.

Formula

Du Bois: BSA = 0.007184 × W^0.425 × H^0.725 · Mosteller: BSA = √(W × H ÷ 3600)

W

weight in kg

H

height in cm

BSA

body surface area in m²

Table of average BSAs

Typical values are shown below. Actual BSA varies widely with build; a tall, heavy adult can exceed 2.5 m², while a newborn is around a tenth of that.

Because BSA is estimated rather than measured, researchers have proposed many formulas, each fitted to a different set of people. They agree closely for adults of average size and drift apart for children, very tall people and people with obesity.

Du Bois and Du Bois (1916) is the oldest and still the most widely used. It was derived from just nine people, whose body surfaces were measured with paper molds, yet it has held up well for adults of normal build. Takahira (1925) used the same structure with coefficients fitted to Japanese adults.

Mosteller (1987) simplified the calculation to the square root of height times weight divided by 3,600. It is easy to compute by hand and gives results close to Du Bois for adults, so it has become a common choice in oncology and pediatrics.

Haycock (1978) and Gehan and George (1970) were developed using data that included infants and children, which makes them a popular choice when dosing drugs for young patients. Boyd (1935) adjusts the weight exponent as weight changes, which helps it fit across a wide range of body sizes, from newborns to adults.

Fujimoto (1968) was derived from Japanese subjects, while Shuter and Aslani (2000) revisited the original Du Bois data with modern statistics. Schlich (2010) used three-dimensional body scans of adults and is the only formula here with separate equations for men and women.

For a man who is 5 feet 9 inches tall and weighs 155 pounds, seven of the formulas give about 1.83 to 1.87 m², while Fujimoto and Schlich come out a little lower at about 1.80 and 1.77 m². For the vast majority of clinical uses, a difference of a few hundredths of a square meter does not matter, but for people at extremes of size, clinicians may choose a specific formula or cap the BSA used for dosing.

Frequently asked questions

Sources

• NIH NCI – Dictionary of Cancer Terms: body surface area
• NIH NLM – MedlinePlus