This calculator gives general estimates for information only. It does not replace advice from your doctor, pharmacist or another qualified health professional.
What body surface area is used for
Body surface area (BSA) is the estimated area of the skin, in square meters. Doctors use it rather than weight to dose some drugs, especially chemotherapy, because it tracks metabolic rate and kidney function better across body sizes. It is also used to index cardiac output (the cardiac index), kidney function (eGFR is expressed per 1.73 m², the BSA of an average adult) and burn treatment. An average adult is around 1.7 to 1.9 m² for women and 1.9 to 2.1 m² for men.
The formulas
All three use weight in kilograms and height in centimeters; the calculator converts pounds and inches.
- Mosteller (1987): BSA = √(height × weight ÷ 3,600). Simple and the most common today.
- DuBois and DuBois (1916): BSA = 0.007184 × weight^0.425 × height^0.725. The historical reference, built from only nine people.
- Haycock (1978): BSA = 0.024265 × weight^0.5378 × height^0.3964. Validated in infants and children as well as adults.
For a normal build, they agree within a few hundredths of a square meter; the gaps grow at the extremes of weight.
Worked example: 170 lb, 5 ft 9 in
- Convert: 170 lb = 77.1 kg and 69 in = 175.3 cm.
- Mosteller: √(175.3 × 77.1 ÷ 3,600) = √3.754 = 1.94 m².
- DuBois: 1.93 m²; Haycock: 1.95 m².
- The BMI for this person is 25.1.
BSA at other weights (height 5 ft 9 in)
| Weight | Mosteller | DuBois |
|---|---|---|
| 110 lb | 1.56 m² | 1.60 m² |
| 140 lb | 1.76 m² | 1.78 m² |
| 170 lb | 1.94 m² | 1.93 m² |
| 200 lb | 2.10 m² | 2.07 m² |
| 250 lb | 2.35 m² | 2.27 m² |
BSA rises much more slowly than weight: going from 140 to 250 lb (+79%) increases BSA by about a third.
Good to know
- Dosing in m²: a drug prescribed at 100 mg/m² means 194 mg for a BSA of 1.94 m². Many oncology teams cap BSA at 2.0 or 2.2 m² for some drugs, and recalculate it when weight changes by more than 5 to 10%.
- Children: pediatric doses often use BSA because a child’s metabolism differs from a scaled-down adult.
- Accuracy: use a recent, measured weight and height. A 2 inch error on height moves BSA by about 1.5%.