A body surface area calculator estimates the total surface area of your body in square metres from your height and weight. This tool shows all four standard published formulas - Mosteller, Du Bois, Haycock and Gehan-George - with Mosteller as the headline, since it is the simplest and most used. BSA is a body measurement, not a diagnosis.
BSA - Mosteller (most used)
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How to Use the Body Surface Area Calculator
- Enter your height. Type the number, then pick cm or in. Inches are converted to centimetres by multiplying by 2.54.
- Enter your weight. Type the number, then pick kg or lb. Pounds are converted to kilograms by dividing by 2.2046226.
- Read all four results. Mosteller is shown as the headline, with Du Bois, Haycock and Gehan-George beside it for comparison.
| Result | What it means |
|---|---|
| BSA - Mosteller | The headline estimate in square metres (m2), from the simplest and most used formula. |
| BSA - Du Bois | The Du Bois and Du Bois estimate, the other most widely used formula. |
| BSA - Haycock | The Haycock estimate, often used across adults and children. |
| BSA - Gehan-George | The Gehan and George estimate, derived from a large sample. |
| Height and weight used | The metric height and weight the formulas used, after any conversion. |
This is an educational estimate. It is not medical advice, a diagnosis, or a drug dose.
What Is Body Surface Area?
Body surface area, or BSA, is the total surface area of the outside of the human body, reported in square metres (m2). It is a measure of body size that combines height and weight into a single figure.
Measuring the real surface area of a body directly is difficult, so it is estimated from height and weight using a published formula. Several formulas exist because different researchers fitted equations to different groups of people.
BSA is used in some areas of medicine and physiology. It appears in cardiac index, in some kidney and metabolic calculations, and in some drug-dosing references. A commonly quoted average for an adult is about 1.7 m2, though real values vary widely with body size.
BSA is a body measurement, like height or weight. On its own it is not a health score, and there is no good or bad BSA. Any clinical use of it belongs to a qualified professional.
How Does the BSA Calculator Work?
The calculator runs all four standard BSA formulas with the same height in centimetres and weight in kilograms, then reports each result in square metres. Mosteller is shown first because it is the simplest and the most used.
BSA = sqrt( (height_cm x weight_kg) / 3600 )BSA = 0.007184 x weight_kg^0.425 x height_cm^0.725BSA = 0.024265 x weight_kg^0.5378 x height_cm^0.3964BSA = 0.0235 x weight_kg^0.51456 x height_cm^0.42246| Formula | Year | Form |
|---|---|---|
| Mosteller | 1987 | Square-root form, easiest to compute |
| Du Bois and Du Bois | 1916 | Power form, the original and still widely used |
| Haycock, Schwartz, Wisotsky | 1978 | Power form, validated in adults and children |
| Gehan and George | 1970 | Power form, fitted to a large sample |
- Convert to metric. Inches are multiplied by 2.54 and pounds divided by 2.2046226, so every formula uses cm and kg.
- Apply each formula. Mosteller takes a square root; the other three raise weight and height to fixed powers.
- Report in square metres. Each result is rounded to two decimals for display.
BSA Example: 180 Cm and 75 Kg
Take a person 180 cm tall weighing 75 kg. Each formula is applied to the same numbers.
- Mosteller: sqrt((180 x 75) / 3600) = sqrt(3.75) = 1.9365, shown as 1.94 m2.
- Du Bois: 0.007184 x 75^0.425 x 180^0.725 = 1.9424, shown as 1.94 m2.
- Haycock: 0.024265 x 75^0.5378 x 180^0.3964 = 1.9381, shown as 1.94 m2.
- Gehan-George: 0.0235 x 75^0.51456 x 180^0.42246 = 1.9438, shown as 1.94 m2.
At this height and weight the four formulas agree closely, all rounding to 1.94 m2. They can differ more at the extremes of body size, which is why this tool shows all four. This case is loaded as the first preset.
Typical BSA Reference Points
| Group | Rough BSA (m2) |
|---|---|
| Average adult (commonly quoted) | About 1.7 |
| Average adult man | About 1.9 |
| Average adult woman | About 1.6 |
| Newborn | About 0.25 |
These are rough reference points only. Your own value depends on your height and weight and the formula used.
Comparing the BSA Formulas: Which to Use
There is no single official BSA formula. The choice depends on the setting, and many references or protocols name the one they expect.
Mosteller
Published in the New England Journal of Medicine in 1987, Mosteller uses a simple square root and is easy to compute by hand or calculator. It is the most widely used today and is the headline result here.
Du Bois and Du Bois
The original 1916 formula. It remains one of the two most widely used and is the one many older references and some dosing tables assume.
Haycock
Published in 1978, Haycock, Schwartz and Wisotsky validated their formula across a wide range of sizes including infants and children, so it is common in paediatric work.
Gehan and George
Published in 1970 and fitted to a large sample of direct measurements. It is a well-regarded power-form alternative.
If a protocol, reference or prescriber specifies a formula, use that one. Our BMI calculator and ideal weight calculator cover other common body measures.
Factors That Change a BSA Result
Each formula was fitted to a different set of real body measurements, so their coefficients differ. At average heights and weights they tend to agree within a few percent, as the worked example shows.
| Factor | Effect on the estimate |
|---|---|
| Very tall or short | The height exponents differ, so the spread between formulas widens. |
| Very high or low weight | The weight exponents differ, so results move apart at the extremes. |
| Children and infants | Formulas validated on children, such as Haycock, may suit small bodies better. |
| Body shape | No height-and-weight formula captures individual body shape, so all are estimates. |
Because the estimates differ, a clinical use should stick to the single formula the reference or protocol names, rather than mixing values from different formulas.
When to Use a BSA Calculator
Checking a Reported Value
A lab report, chart or reference may list a BSA. This tool lets you reproduce it and see which formula matches.
Cardiac and Physiology Indexes
Measures such as cardiac index are reported per square metre of BSA. This tool gives the BSA that such an index would divide by.
Comparing Formulas
Seeing all four side by side shows how much the choice of formula changes the number for a given height and weight.
Study and Teaching
Students can check a coursework answer against the published formulas and coefficients shown here.
For related body measures, see our lean body mass calculator and waist to height ratio calculator.
Common Mistakes with BSA
1. Calculating a Drug Dose from It
BSA appears in some dosing references, but working out a dose is a clinical decision. The prescriber chooses the formula, the reference and the dose. Do not dose from this tool.
2. Mixing Units
Entering height in inches while the unit says cm, or weight in pounds while it says kg, gives a wrong result. Set each unit to match your number.
3. Expecting One True Value
There is no single correct BSA. The formulas differ by design, so a small spread between them is normal.
4. Reading It as a Health Score
BSA is a body size measure, not a measure of health. A larger or smaller BSA is not good or bad on its own.
5. Mixing Formulas in One Calculation
If a reference expects Du Bois, use Du Bois throughout. Do not swap in a value from another formula partway through.
6. Using It Beyond a Sensible Range
The formulas were fitted to real human sizes. Values far outside the normal range are less reliable.
Accuracy and Limitations
The calculator reproduces the four published formulas and their coefficients exactly. The limits lie in what a height-and-weight estimate of surface area can tell you.
What it calculates accurately
- The Mosteller, Du Bois, Haycock and Gehan-George BSA from height and weight.
- The worked example: all four round to 1.94 m2 at 180 cm and 75 kg.
- The in-to-cm conversion (x2.54) and the lb-to-kg conversion (divide by 2.2046226).
- Results in square metres, rounded to two decimals.
What it does not account for
- Individual body shape, which no height-and-weight formula captures.
- Which formula a specific reference, protocol or prescriber requires.
- Drug dosing, which is a clinical decision for the prescriber.
- Unusual body sizes far outside the range the formulas were fitted to.
This is not medical advice and not a dose. For any clinical use, confirm the value and the chosen formula with a qualified professional.
How We Calculate Body Surface Area
Frequently Asked Questions About Body Surface Area
What is body surface area?
Body surface area, or BSA, is the total surface area of the body in square metres, estimated from height and weight. It is a measure of body size used in some medical and physiology calculations.
Which BSA formula is most used?
Mosteller and Du Bois are the two most widely used. Mosteller is the simplest, using a square root, and is the headline result here. If a reference or protocol names a formula, use that one.
What is the average body surface area?
A commonly quoted average for an adult is about 1.7 m2. Real values vary widely with height and weight, so your own result may be higher or lower.
Why do the four formulas give different results?
Each was fitted to a different set of real measurements, so their coefficients differ. They usually agree within a few percent at average sizes and spread apart at the extremes of height and weight.
Can I use this BSA calculator for children?
The tool accepts small heights and weights, and the Haycock formula was validated in children. It does not give paediatric dosing, which is a clinical decision for a qualified prescriber.
Should I use BSA to work out a drug dose?
No. BSA appears in some dosing references, but calculating a dose is a clinical decision. The prescriber chooses the formula, the reference and the dose for each patient.
How do I convert height and weight for BSA?
The tool converts for you. Inches are multiplied by 2.54 to get centimetres, and pounds are divided by 2.2046226 to get kilograms, before the formulas run.
Is there a single correct BSA value?
No. BSA is an estimate and the formulas differ by design, so a small spread between them is normal. A clinical use should stick to the one formula the reference specifies.
Is a higher or lower BSA better?
Neither. BSA is a body size measurement, not a health score. There is no good or bad value, and it should not be read as a measure of health.
Is my data saved?
No. The math runs in your browser. The Save button keeps results only in your own browser storage.
Sources
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med 1987;317:1098 (Mosteller formula; accessed 2026-10-05).
- Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area. J Pediatr 1978;93:62-66 (Haycock formula; accessed 2026-10-05).
- Gehan EA, George SL. Estimation of human body surface area from height and weight. Cancer Chemother Rep 1970;54:225-235 (Gehan and George formula; accessed 2026-10-05).
- Body Surface Area. StatPearls, NCBI Bookshelf (clinical reference, incl. Du Bois 1916 and formula corroboration; accessed 2026-10-05).
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Explore all health calculatorsEducational estimate only, not medical advice, diagnosis, or a dosing instruction. Body surface area is used in some drug-dosing and physiology contexts, but dosing decisions belong to the prescriber, who uses the method, the reference and the clinical picture for each patient. Different formulas give slightly different values. Do not calculate or change any medicine dose from this tool. Confirm any clinical use with a qualified healthcare professional. Spotted an error? Let us know.
Author
Shakeel Muzaffar is the Founder and Editor-in-Chief of MultiCalculators.com, bringing over 15 years of experience in digital publishing, product strategy, and online tool development. He leads the platform's editorial vision, ensuring every calculator meets strict standards for accuracy, usability, and real-world value. Shakeel personally oversees content quality, formula verification workflows, and the platform's commitment to publishing tools that are genuinely useful for students, professionals, and everyday users worldwide.
