Body Surface Area Calculator
Enter your height and weight to estimate your body surface area (BSA) using the Mosteller and Du Bois formulas.
Mosteller BSA
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The Mosteller result is shown as the headline because it is simple and widely used in clinical settings. The Du Bois result is shown for comparison, and the two formulas usually agree closely.
A body surface area calculator estimates the total surface area of your body in square metres, based on your height and weight. It is one of the most useful numbers in medicine, because many drug doses, fluid rates, and heart and kidney measurements are scaled to body size rather than to weight alone.
What Is Body Surface Area?
Body surface area (BSA) is the total area of the outside of your body. For an average adult it is about 1.7 to 1.9 square metres, roughly the area of a single bedsheet. BSA is used because it tracks closely with blood volume, metabolic rate, and organ size, often more closely than weight does on its own.
BSA is not something you can measure directly with a tape measure at home. Instead, it is estimated from height and weight using formulas fitted to measured data. The two most common formulas are Mosteller and Du Bois, and both are built into the calculator above.
How to Use This Body Surface Area Calculator
- Choose your unit system: metric (cm and kg) or imperial (feet, inches, and lb).
- Enter your height. In metric mode, enter your height in centimetres. In imperial mode, enter feet and inches separately.
- Enter your weight in kilograms or pounds, matching the unit system you chose.
- Click Calculate BSA.
- Read your Mosteller BSA as the headline result, with the value in square centimetres and the Du Bois result shown for comparison.
For the best result, measure your height without shoes and weigh yourself on a flat, hard surface.
The Mosteller and Du Bois Formulas
The Mosteller formula is the simplest of the two and the one most clinicians reach for first:
BSA = square root of (height in cm x weight in kg / 3600)
The result is in square metres. To convert it to square centimetres, multiply by 10,000.
The Du Bois formula is older and slightly more complex:
BSA = 0.007184 x weight in kg to the power 0.425 x height in cm to the power 0.725
Both formulas were fitted to measurements from real people, and they agree closely for most adults. The calculator shows both so you can see how little they differ in practice.
Body Surface Area Calculator: Verified Examples
These examples were checked against the formulas above, so you can confirm the calculator is giving the right answer:
| Height | Weight | Mosteller BSA | Mosteller in cm2 | Du Bois BSA |
|---|---|---|---|---|
| 170 cm | 70 kg | 1.82 m2 | 18,181 cm2 | 1.81 m2 |
| 180 cm | 80 kg | 2.00 m2 | 20,000 cm2 | 2.00 m2 |
| 160 cm | 55 kg | 1.56 m2 | 15,635 cm2 | 1.56 m2 |
Check the first row by hand: square root of (170 x 70 / 3600) = square root of 3.3056 = 1.82, rounded to two decimal places. Multiply by 10,000 and you get 18,181 square centimetres.
Why Does Body Surface Area Matter?
Many cancer chemotherapy doses are calculated per square metre of body surface area, because the amount of drug a body can handle depends more on overall size than on weight alone. The same idea applies to some other medicines, to fluid replacement in burns, and to cardiac output measurements.
BSA is also used to index heart and kidney measurements. For example, an echocardiogram may report cardiac index, which is cardiac output divided by BSA, so that hearts of different-sized people can be compared fairly. Kidney function estimates may likewise be standardised to a BSA of 1.73 square metres, the reference value for an average adult.
For everyday use, BSA is simply a more complete picture of body size than weight on its own. Two people can weigh the same yet have different BSAs if their heights differ, and that difference can matter when a dose or a measurement depends on size.
Limitations to Keep in Mind
BSA formulas are estimates fitted to average populations. They are less accurate for people with unusual body shapes, for amputees, and for children, where specialised formulas or direct measurements may be preferred. The Du Bois formula in particular was based on a small group of adults, so it should be treated as an approximation rather than an exact measurement.
Do not use a BSA result to set a medicine dose yourself. Dosing decisions belong to a clinician, who will also consider kidney and liver function, other medicines, and your full medical history. This calculator is for information only.
Frequently Asked Questions
What is a normal body surface area?
For an average adult, BSA is usually between 1.6 and 2.0 square metres. Men tend to be slightly higher than women because they are on average taller and heavier. Children have much smaller BSAs, often below 1 square metre.
Is Mosteller or Du Bois more accurate?
For most adults the two formulas differ by only a few hundredths of a square metre, so either is fine for general use. Mosteller is preferred in many clinical settings because it is simpler and easy to check by hand. Du Bois is sometimes used in research where a long-established reference value is needed.
Can I calculate BSA from imperial units?
Yes. Choose the imperial option in the calculator and enter your height in feet and inches and your weight in pounds. The calculator converts them to centimetres and kilograms first, then applies the same formulas.
Does BSA change with weight loss?
Yes. Because BSA depends on both height and weight, losing or gaining weight changes it. A 10 kg weight change typically moves BSA by about 0.1 to 0.15 square metres, depending on your height.
Is BSA the same as BMI?
No. BMI divides weight by height squared and gives a single number used to classify underweight, healthy weight, overweight, and obesity. BSA is an estimate of your total skin surface area in square metres, used mainly for dosing and for indexing heart and kidney measurements.
Can children use this calculator?
The formulas work mathematically for children, but they were developed and validated mainly in adults. For children, clinicians often use age-specific charts or formulas, so treat a result for a child as a rough guide only and ask a clinician for anything that matters.
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