Body Surface Area Calculator
Calculate body surface area in m² with nine formulas side by side, including Mosteller, Du Bois and Haycock, plus dose per m² and cardiac index.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Body Surface Area Calculator?
The Body Surface Area Calculator estimates the outer surface of the human body in square metres from height and weight. It runs nine published equations at once: Mosteller, Du Bois and Du Bois, Haycock, Gehan and George, Boyd, Fujimoto, Takahira, Shuter and Aslani, and the sex-specific Schlich equations. You pick the headline formula, and the table shows how far the others agree.
BSA matters because many clinical numbers are scaled by it. Chemotherapy doses are written in mg/m², cardiac output becomes cardiac index when divided by BSA, and kidney function is reported per 1.73 m². Two optional fields turn the result into a dose for a per-m² amount and into a cardiac index, so you can check a calculation you have been given.
Height can be entered in centimetres or feet and inches, weight in kilograms or pounds. Everything runs in your browser and nothing is stored.
- Nine BSA formulas in one table with your selection highlighted
- Metric or US units with automatic conversion
- Optional dose per m² and cardiac index
- Paediatric warning for adult-only formulas
- Copyable summary and shareable link
- Runs in your browser; nothing is stored
How to use the Body Surface Area Calculator
- Choose metric or US units. Switching converts the values already entered.
- Enter height and weight. Select the sex only if you want the Schlich equations, which differ for women and men.
- Pick the headline formula. Mosteller is the default because most dosing software uses it; click any row in the table to switch.
- Optionally type a dose per m² (for example 75 for 75 mg/m²) to get a total dose, or a cardiac output in L/min to get cardiac index.
- Copy the result, or open How this was calculated to see Mosteller worked with your numbers.
Worked examples
Average adult
Input
170 cm, 70 kg
Output
Mosteller 1.82 m², Du Bois 1.81 m², range 1.70 to 1.83 m² across all nine
√(170 × 70 / 3600) = 1.818. The low end of the range is Schlich for men; the classic formulas all sit between 1.76 and 1.84.
Dose per square metre
Input
170 cm, 70 kg, dose 75 per m²
Output
Dose 136.5
The page multiplies 75 by the BSA rounded to 2 decimals, 1.82 m². Hospital protocols set their own rounding and caps, so treat this as a check, not a prescription.
Child
Input
110 cm, 18 kg
Output
Mosteller 0.74 m², Haycock 0.74 m², Schlich 0.59 m²
Mosteller, Du Bois and Haycock agree closely, but the adult-derived Schlich equation reads far too low. The page warns about this below 150 cm.
Background and insight
Eugene and Delafield Du Bois published the first practical BSA equation in 1916 after covering nine people in paper moulds and measuring the pieces. Their result, 0.007184 × W^0.425 × H^0.725, became the standard for a century despite the tiny sample. Edith Boyd collected several hundred direct measurements in 1935, and in 1970 Gehan and George refitted 401 of them to give 0.0235 × W^0.51456 × H^0.42246. In 1978 Haycock, Schwartz and Wisotsky produced an equation validated from newborns to adults, which is why paediatric units often prefer it.
In 1987 Raymond Mosteller pointed out in a one-paragraph letter to the New England Journal of Medicine that the Gehan and George equation is almost exactly the square root of height × weight / 3600. That version can be done on a pocket calculator, and it is now the most widely used formula for drug dosing. For an average adult the main formulas agree within 2 to 3%; they spread further for small children, very tall people and obesity.
Dosing by BSA is a convention, not a law of pharmacology. It became standard for cytotoxic drugs in the 1950s because toxic doses scaled better between species by surface area than by weight. Some drugs now use other rules: carboplatin is dosed with the Calvert formula from kidney function, and the American Society of Clinical Oncology recommends using actual body weight, not a capped BSA, for most adults with obesity.
Common use cases
Checking chemotherapy calculations
Nurses, pharmacists and patients can confirm the BSA and mg/m² arithmetic on a treatment plan.
Cardiac index
Divide cardiac output from an echo or catheter study by BSA to compare hearts of different sizes.
Indexing lab and imaging values
Left ventricular mass, valve areas and eGFR are often reported per m² or per 1.73 m².
Teaching and research
Compare how nine equations behave at the extremes of size before choosing one for a study.
Tips and limitations
- Use the formula your protocol or software specifies. Switching formulas mid-treatment changes the dose by a few percent for no clinical reason.
- Weigh and measure on the day. A 5 kg change moves BSA by about 3 to 4% in an adult.
- Fujimoto, Takahira and Schlich were fitted to adults; for children use Haycock or Mosteller.
- BSA is unrelated to burn size estimates. Burns are expressed as a percentage of total body surface with the rule of nines or a Lund and Browder chart.
- For people with obesity, oncology guidelines recommend full weight-based BSA unless there is a specific reason to cap it. That decision belongs to the treating team.
Frequently asked questions
Which BSA formula should I use?
Use whichever your hospital or protocol specifies. Mosteller is the most common for drug dosing because it is simple and close to Gehan and George. Du Bois is still used in many cardiology and physiology labs, and Haycock is popular in paediatrics.
What is a normal body surface area?
US survey data (NHANES 2011 to 2014) put the average at about 2.06 m² for adult men and 1.83 m² for adult women. The 1.73 m² used to normalise kidney function is an average adult value from the 1920s, kept for consistency.
How do I calculate BSA by hand?
With Mosteller, multiply height in cm by weight in kg, divide by 3600 and take the square root. For 170 cm and 70 kg: 170 × 70 = 11,900; divided by 3600 is 3.306; the square root is 1.82 m².
How is a dose in mg/m² turned into milligrams?
Multiply the per-m² dose by BSA. 75 mg/m² for a 1.82 m² person is 136.5 mg. Protocols then apply rounding, dose caps and adjustments for kidney or liver function, which this calculator does not do.
Why do the formulas give different answers?
Each was fitted to a different group of people with different measuring methods, from paper moulds in 1916 to much larger modern datasets. They agree within a few percent for typical adults and diverge for children, very tall people and high body weights.
Is BSA used for burns?
Not in this way. Burns are described as a percentage of total body surface area using the rule of nines or Lund and Browder charts, and fluid formulas then use body weight. This calculator gives absolute area in square metres.
What is cardiac index?
Cardiac output divided by BSA, in L/min/m². It lets clinicians compare heart pumping across body sizes; a resting value of roughly 2.5 to 4.0 is typical in adults.
Is there an in-depth guide to the Body Surface Area Calculator?
Yes. “Body Surface Area Formulas: Mosteller, Du Bois and Why They Differ” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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