Body Surface Area Calculator
Body surface area sounds like a geometry problem, but in practice it is a dosing number. Chemotherapy orders, cardiac index readings and kidney function reports are all scaled to the surface area of the body in square meters, and a small error in that figure carries straight into the dose. This body surface area calculator takes height and weight in metric or imperial units and runs all six established formulas at once, so you can see the primary result and how far the alternatives sit from it.
Pick the formula your protocol uses as the primary result. The calculator then shows the other five alongside it: DuBois and DuBois, Mosteller, Haycock, Boyd, Gehan and George, and Fujimoto. For a typical adult the six agree within a few hundredths of a square meter. At the extremes of size they pull apart, and that spread is exactly what a single-formula tool hides from you.
For information only. This calculator is not medical advice and must not be used on its own to set a medication dose. Dosing decisions belong with a qualified clinician using your full clinical picture.
Quick Answer
Key takeaways
- All six formulas are calculated every time. The primary formula setting only chooses which result is headlined, so you can compare protocols without re-entering anything.
- For average-sized adults the formulas agree within about 0.02 to 0.07 m2. The gaps that matter show up in small children and in very large bodies.
- BSA feeds dose and physiology calculations, it does not replace them. A dose still needs the drug, the protocol and a clinician.
- Consistency beats formula shopping: for one patient, one service should use the same formula every time.
- Quick Answer
- How to use this body surface area calculator
- The six BSA formulas and where each one came from
- Worked example: 170 cm and 70 kg through all six formulas
- What a BSA number is actually used for
- BSA is not BMI, and the difference matters
- What competing calculators miss
- Frequently asked questions
- Add This Calculator to Your Website
- References
How to use this body surface area calculator
Enter height and weight in whichever units you have them, pick the unit next to each value, then choose the primary formula your setting uses. Click Calculate BSA.
The results open with your converted measurements in centimeters and kilograms, the headline BSA for the primary formula, and a table of all six results. Check the conversions first: most BSA errors in practice are unit errors, a height entered in inches against a centimeter setting, rather than formula errors. If the converted height and weight look wrong, the BSA will be wrong no matter which formula headlines it.
The six BSA formulas and where each one came from
Every formula here estimates the same thing from the same two inputs, height in centimeters and weight in kilograms, and returns square meters. They differ because each was fitted to a different set of measured bodies, in a different era, with different mathematics.
| Formula | Equation | Built from | Where it earns its place |
|---|---|---|---|
| DuBois and DuBois (1916) | 0.007184 x height^0.725 x weight^0.425 | Direct surface measurements of 9 subjects | The most widely cited formula in medicine and the default here |
| Mosteller (1987) | Square root of (height x weight / 3600) | A simplification published in the New England Journal of Medicine | Routine clinical use; the only one you can check by hand |
| Haycock (1978) | 0.024265 x height^0.3964 x weight^0.5378 | 81 people from premature infants to adults, measured geometrically | Children and small bodies, where DuBois runs low |
| Boyd (1935) | 0.0003207 x height^0.3 x weight in grams^(0.7285 minus 0.0188 x log10 of weight in grams) | A growth study of surface area across body sizes | Extremes of size; its weight exponent shifts with body mass |
| Gehan and George (1970) | 0.0235 x height^0.42246 x weight^0.51456 | 401 direct BSA measurements | Chemotherapy research, where it was published for dose work |
| Fujimoto (1968) | 0.008883 x height^0.663 x weight^0.444 | Japanese subjects | Comparison in Japanese practice; tends to read slightly lower |
Two of these deserve a straight warning. DuBois rests on nine subjects, all adults, measured in 1916. It has survived because it works well for typical adults, not because its evidence base is strong, and later studies found it underestimates below about 0.7 m2. Boyd is the opposite problem: a thoughtful formula whose moving exponent makes it the hardest to verify by hand, which is one reason it is rarely a service’s default.
Worked example: 170 cm and 70 kg through all six formulas
The calculator is pre-filled with this case, and every figure below is what it returns: 170 cm, 70 kg, DuBois and DuBois as the primary formula.
| Formula | Result |
|---|---|
| DuBois and DuBois: 0.007184 x 170^0.725 x 70^0.425 | 1.81 m2 |
| Mosteller: square root of (170 x 70 / 3600) = square root of 3.3056 | 1.82 m2 |
| Haycock | 1.83 m2 |
| Boyd | 1.83 m2 |
| Gehan and George | 1.83 m2 |
| Fujimoto | 1.76 m2 |
The spread from lowest to highest is 0.07 m2, about 4 percent of the value. Hand-check the Mosteller line and you can trust the set: 170 x 70 is 11,900, divided by 3,600 is 3.3056, and the square root of 3.3056 is 1.82. Fujimoto sitting a touch lower is its known behavior on body proportions outside the population it was fitted to, not a bug in the arithmetic.
What a BSA number is actually used for
A BSA value is an input to other clinical calculations, never an answer on its own. The best known use is chemotherapy dosing, where many cytotoxic drugs are ordered per square meter: a protocol dose of 75 mg/m2 against the worked example’s DuBois result gives 75 x 1.81, about 135.8 mg before the clinical team applies the protocol’s rounding, capping and organ-function rules. General medicine dosage calculations follow the same pattern of scaling an order to the patient in front of you, and BSA is the scaling factor oncology settled on.
Outside oncology, cardiac index is cardiac output divided by BSA, which lets clinicians compare heart performance between a small adult and a large one. Kidney function estimates are reported per 1.73 m2, the reference surface area, so results from different bodies sit on one scale. Burn care uses surface area percentages to size fluid resuscitation. In pediatrics, where doses are often scaled down from adult doses by surface area, a pediatric-specific check such as the amoxicillin dose calculator still starts from an accurate size estimate for the child.
BSA is not BMI, and the difference matters
The two numbers are confused constantly because both come from height and weight. They answer different questions and they are not interchangeable in any formula.
Body surface area (BSA)
- Units: square meters (m2)
- Estimates the skin surface of the body
- Used for: drug dosing per m2, cardiac index, kidney function scaling
- Worked example value: 1.81 m2 (DuBois)
Body mass index (BMI)
- Units: kg/m2, an index rather than an area
- Estimates body fatness for screening
- Used for: weight category screening and population statistics
- Same person: 70 / 1.70^2 = 24.22
Entering a BMI where a protocol asks for BSA, or the reverse, is a quiet and serious error. If a number near 24 appears in a dosing calculation that expected a number near 1.8, stop and check which index was actually asked for.
What competing calculators miss
Most BSA tools on the web run two formulas, usually DuBois and Mosteller, and present one number as if the question were settled. Three gaps follow from that.
Gap 1: no view of formula disagreement. Two formulas agreeing proves little, because DuBois and Mosteller were always close for typical adults. The honest test is the full set, including Boyd and Fujimoto, which is why this calculator computes all six on every run and shows the spread instead of hiding it.
Gap 2: no help at the extremes. The cases where formula choice changes a dose are small children and very large adults, and those are the cases a two-formula tool says nothing about. Haycock exists for the small end and Boyd for the extremes; a tool that omits them leaves its user with the formulas least suited to the patient.
Gap 3: silent unit handling. Several tools accept feet and inches as a single decimal entry, or convert pounds with a rounded factor and never show the converted values. This calculator prints the converted height and weight in centimeters and kilograms at the top of the results, so a unit slip is visible before the BSA is used for anything.
Frequently asked questions
DuBois and DuBois is the most widely cited and is the default primary formula here. Mosteller is the simplest and is recommended by some cancer programs for routine use. Haycock is preferred for small children. For one patient, use the same formula consistently rather than switching between visits.
Each was fitted to different measurement datasets with different mathematics. They agree closely for average-sized adults, usually within 1 to 3 percent, and diverge more for very small or very large bodies, which is where the choice of formula starts to matter.
About 1.6 to 1.9 m2 covers most adults, roughly 1.6 m2 for an average adult woman and 1.9 m2 for an average adult man. The calculator flags your primary result as below, within, or above that range. A value outside it is not automatically a problem; tall and heavy adults sit above it by arithmetic alone.
The formulas work mathematically for children, and Haycock was built partly for them. Interpretation differs, though: a 9-year-old averages about 1.07 m2 and a 10-year-old about 1.14 m2. Pediatric dosing must always be set by a clinician, never from a calculator result alone.
No. BMI is weight divided by height squared, a screening index for body fatness. BSA estimates the surface area of the skin in square meters and is used for dosing and physiology calculations. The two numbers are not interchangeable in any formula.
The original 1916 study measured only nine subjects, all adults. Later work found the formula runs low below about 0.7 m2, which is one reason alternatives such as Haycock, fitted on infants and children as well as adults, were developed.
Yes. Every formula takes current weight as an input, so gaining or losing weight changes the result, and services recalculate BSA before each BSA-based treatment cycle. Use a current weight, not the weight from an old chart entry.
No. BSA is one input into a dosing decision that also depends on the drug, the protocol, kidney and liver function, and prior treatment. This calculator is for information and checking. Final doses are set by the prescribing clinician.
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References
- Du Bois D, Du Bois EF, “A formula to estimate the approximate surface area if height and weight be known,” Archives of Internal Medicine, 1916. The original nine-subject study behind the most widely used BSA formula. Bibliographic record and formula discussion in the comparison study below. Accessed October 2026.
- Mosteller RD, “Simplified calculation of body-surface area,” New England Journal of Medicine, 1987;317:1098. The paper that introduced the square root formula used for routine clinical BSA. Accessed October 2026.
- Haycock GB, Schwartz GJ, Wisotsky DH, “Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults,” Journal of Pediatrics, 1978. Source of the Haycock formula and its pediatric validation. Accessed October 2026.
- Gehan EA, George SL, “Estimation of human body surface area from height and weight,” Cancer Chemotherapy Reports, 1970. The 401-measurement dataset behind the Gehan and George formula. Accessed October 2026.
- Verbraecken J and colleagues, “Body surface area in normal-weight, overweight, and obese adults: a comparison study,” Metabolism, 2006. Compares DuBois, Mosteller, Boyd, Gehan and George and Haycock against measured values across body sizes. Comparison of BSA formulas in adults at extremes of height and weight. Accessed October 2026.
- SISMED (Italian Society of Internal Medicine), “Body Surface Area (BSA): Du Bois and Mosteller.” Clinical summary of BSA formulas and their use in pharmacology, including methotrexate, cyclophosphamide and doxorubicin dosing. SISMED: Body Surface Area, Du Bois and Mosteller. Accessed October 2026.