What Is Body Surface Area and Why It Matters

Body surface area, or BSA, is the total area of your skin, measured in square meters. Medicine uses it because body size shapes how some treatments are scaled, and because it behaves more evenly than weight alone across different body types.

What Is Body Surface Area?

Body surface area is an estimate of the total outer area of your skin, written in square meters (m2). It combines height and weight into one number that reflects overall body size better than weight on its own.

You cannot roll out your skin and measure it with a ruler. So researchers built formulas that estimate BSA from height and weight, which are easy to record. These formulas come from careful studies going back more than a century, and they still guide practice today.

BSA is a size measure, not a health grade. It does not tell you if a body size is healthy, and it says nothing about body fat. For those questions, people use other tools, such as the BMI calculator. BSA simply answers one question: how much surface does this body have?

How Is Body Surface Area Calculated?

The short answer: most clinicians use the Mosteller formula, published in 1987. It is popular because it is simple enough to check by hand yet accurate enough for routine use. You take height in centimeters, multiply by weight in kilograms, divide by 3600, then take the square root.

Here is a worked example. Take a person who is 180 cm tall and weighs 75 kg. Multiply 180 by 75 to get 13,500. Divide by 3600 to get 3.75. The square root of 3.75 is about 1.9365, which rounds to 1.94 m2. The diagram below walks through the same steps.

You do not need to run this by hand every time. The body surface area calculator returns your BSA in one step and lets you switch formulas. Enter height and weight, and it does the arithmetic for you.

Why the Four Main BSA Formulas Give Close Results

There is more than one BSA formula, and they land close together for most adults. The four you will see most are Mosteller (1987), Du Bois and Du Bois (1916), Haycock (1978), and Gehan and George (1970). Each was fitted to measured data in its own study.

For our 180 cm, 75 kg example, all four round to the same 1.94 m2. The small gaps before rounding show why clinicians still state which formula they used. The chart below compares the four results side by side.

The table lines up the formulas and where each one fits best.

Because results can differ slightly, the chosen formula is stated when BSA is used for a precise purpose. For everyday understanding, any of the four gives a sound estimate of body size.

Why Medicine Uses Body Surface Area

Medicine uses BSA because many body functions track surface area more closely than body weight. That makes BSA a steadier way to scale certain measurements across people of different sizes.

Here is where it shows up. Some chemotherapy drugs and a few other medicines are scaled to BSA, so the plan reflects body size rather than weight alone. Heart specialists use cardiac index, which is cardiac output divided by BSA, to compare heart output fairly between a small adult and a large one.

• Drug scaling. Some chemotherapy and other doses are set per square meter of BSA. The prescriber makes every dosing decision.
• Cardiac index. Cardiac index equals cardiac output divided by BSA, which standardizes heart output by body size.
• Burns context. BSA helps frame how large an injured area is, but burn care uses separate rules, such as the Wallace Rule of Nines, to estimate the percent of total body surface area burned.

One caution ties the uses together. Because formulas differ a little, the formula is named whenever BSA feeds a precise number. Dosing and clinical choices always belong to a qualified clinician, not to a calculator.

What Is a Typical Adult Body Surface Area?

A typical adult BSA is roughly 1.5 to 2.0 m2. An often-cited average is about 1.7 m2, but treat that as a general reference point, not a target or a rule. Your own number depends on your height and weight.

The range is wide on purpose. Taller and heavier bodies have more surface, and shorter or lighter bodies have less. Children sit below the adult range and grow into it, which is one reason the Haycock formula is popular for younger patients.

Want to place yourself on this line? Run your height and weight through the body surface area calculator, then explore related size measures like the ideal weight calculator and the lean body mass calculator. For more size and health tools, see the health calculators hub.

FAQs About Body Surface Area

Sources and Further Reading

This article is general education, not medical advice. The numbers here are general guidance, not personal targets. Talk to a healthcare provider about your own health. Reviewed for accuracy by Dr. Abdullah Khalil, MBBS. Last updated 2026-10-05.