Body Surface Area Calculator
Estimate body surface area (BSA) in square metres using the Mosteller, Du Bois, Haycock or Gehan & George formula.
Full Breakdown
Comparison Across All Formulas
Body Surface Area Calculator
Our Body Surface Area Calculator estimates BSA in square metres (m²) from your height and weight, using your choice of four validated formulas: Mosteller, Du Bois & Du Bois, Haycock, or Gehan & George. BSA is used in medicine to normalise physiological measurements and to calculate some medication doses, but this calculator is for general information only and is not a substitute for calculations performed by a qualified healthcare professional.
What Is Body Surface Area and Why Does It Matter?
Body surface area is an estimate of the total surface area of the human body, calculated from height and weight rather than measured directly. Several physiological processes — including cardiac output, kidney filtration rate, blood volume and the clearance of many drugs — scale more closely with body surface area than with weight alone. Because of this, clinicians use BSA to normalise measurements like cardiac index and glomerular filtration rate (commonly reported per 1.73 m², a reference adult BSA), and to calculate doses for chemotherapy and certain other medications where the therapeutic window is narrow.
The Four Formulas This Calculator Supports
| Formula | Year | Commonly Used For |
|---|---|---|
| Mosteller | 1987 | A simple and widely used modern formula |
| Du Bois & Du Bois | 1916 | The historical reference formula, still used by some institutions and drug protocols |
| Haycock | 1978 | Validated across infants, children and adults; commonly used in paediatric settings |
| Gehan & George | 1970 | Derived from a larger validation sample spanning a wide range of body sizes |
Mosteller: BSA (m²) = √(height (cm) × weight (kg) / 3600)
Du Bois & Du Bois: BSA (m²) = 0.007184 × weight (kg)0.425 × height (cm)0.725
Haycock: BSA (m²) = 0.024265 × weight (kg)0.5378 × height (cm)0.3964
Gehan & George: BSA (m²) = 0.0235 × height (cm)0.42246 × weight (kg)0.51456
Why Do the Formulas Give Different Answers?
Each formula was derived from a different, relatively small sample of measured subjects, using different measurement and statistical fitting methods. For an average-sized adult, the four formulas typically agree within about 2-5% of each other, but they can diverge by more at the extremes of height and weight. The original Du Bois formula, developed from just 9 subjects in 1916, is known to increasingly underestimate BSA in smaller people, including infants, which is one reason the Haycock formula (validated specifically across infants, children and adults) is often preferred in paediatric settings. Clinical institutions vary in which formula they use by default, and some drug protocols specify a particular formula or require cross-checking between two formulas before a dose is finalised.
Typical BSA Ranges
As a general reference point, average adult BSA is often cited as roughly 1.9 m² for men and 1.6 m² for women, with a commonly used reference value of 1.73 m² for normalising measurements like kidney filtration rate. These are population averages rather than targets, and individual BSA varies considerably with height and weight, as this calculator will show you directly.
Important Limitations
- Not a substitute for clinical calculation. If BSA is being used to calculate a medication dose, that calculation must be performed and verified by a qualified healthcare professional using validated clinical software, not a public web calculator.
- Unit errors matter. Documented dosing errors in clinical practice have occurred from height and weight being entered in the wrong units, or transposed with each other. Always double-check which unit (cm/in, kg/lb) you’re entering.
- Formula choice affects the result. Different formulas can produce results that differ by several percent for the same person, which is clinically meaningful for drugs with a narrow therapeutic window.
- Extreme body sizes. All of these formulas were derived from limited samples and may be less accurate at the extremes of height and weight, including in people with significant oedema, ascites, amputation, or very high or low body weight.
Frequently Asked Questions
What is body surface area used for?
Body surface area (BSA) is used in medicine to normalise physiological measurements that scale more closely with body size than with weight alone, such as cardiac output and kidney filtration rate, and to calculate doses for chemotherapy and some other medications. It is a calculated estimate based on height and weight, not something that’s measured directly on most patients.
Which BSA formula should I use?
Mosteller is the simplest and most commonly used formula in modern clinical practice, and is the default on this calculator. Du Bois is the historical reference formula still used by some institutions. Haycock is generally preferred for infants and children, since it was specifically validated across that age range. If you need a BSA figure for a specific clinical or research purpose, use whichever formula your institution, protocol or clinician specifies, since consistency matters more than which formula is theoretically “best.”
Can I use this calculator to work out a chemotherapy dose?
No. This calculator provides a general BSA estimate for information purposes only. Medication doses based on BSA, including chemotherapy, must be calculated and verified by a qualified healthcare professional using validated clinical software, not a public web calculator. Height and weight measurements used for actual dosing should also be taken under clinical conditions.
Why do different BSA formulas give different results for the same person?
Each formula was derived from a different, relatively small sample of measured subjects using different statistical methods. For an average adult they typically agree within about 2-5%, but can diverge more at the extremes of height and weight. This is one reason clinical protocols often specify exactly which formula must be used, rather than leaving it to individual choice.
What is a normal or average BSA?
Average adult BSA is often cited as roughly 1.9 m² for men and 1.6 m² for women, with 1.73 m² commonly used as a reference value for normalising clinical measurements like kidney filtration rate. These are population averages, not individual targets — your own BSA depends on your height and weight.
Is BSA the same as BMI?
No. Body Mass Index (BMI) is weight divided by height squared, and is used as a general screening measure related to body fatness. Body surface area (BSA) estimates the total surface area of the body and is used differently in medicine, mainly to normalise physiological measurements and calculate certain drug doses. They use similar inputs (height and weight) but are calculated differently and used for different purposes.