The body surface area calculator uses the Mosteller formula — the most widely adopted BSA formula in clinical practice — to compute BSA in square metres from a patient's height and weight. BSA is used when body weight alone is an insufficient basis for drug dosing, particularly in chemotherapy (where dose is expressed as mg/m²), certain paediatric medications, and burn resuscitation assessment. The normal adult BSA range is 1.6–1.9 m².
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| Population | Average BSA |
|---|---|
| Newborn | 0.25 m² |
| Child (2 years) | 0.5 m² |
| Child (10 years) | 1.14 m² |
| Adult female | 1.6 m² |
| Adult male | 1.9 m² |
Body surface area in m², calculated as the square root of (height in cm × weight in kg ÷ 3600). Values are rounded to two decimal places, which is the convention on most dosing charts.
| Height | 50 kg | 60 kg | 70 kg | 80 kg | 90 kg |
|---|---|---|---|---|---|
| 150 cm | 1.44 | 1.58 | 1.71 | 1.83 | 1.94 |
| 160 cm | 1.49 | 1.63 | 1.76 | 1.89 | 2.00 |
| 170 cm | 1.54 | 1.68 | 1.82 | 1.94 | 2.06 |
| 180 cm | 1.58 | 1.73 | 1.87 | 2.00 | 2.12 |
| 190 cm | 1.62 | 1.78 | 1.92 | 2.05 | 2.18 |
Worked through: a patient 170 cm and 70 kg. Multiply 170 × 70 = 11,900, divide by 3,600 = 3.31, then take the square root = 1.82 m². Notice how little BSA moves compared with weight — a 40 kg difference changes it by roughly half a square metre, because the square root compresses the range. That's the whole point of dosing by surface area rather than by weight for drugs with a narrow therapeutic window.
Surface area shows up wherever a dose or a measurement needs to scale with body size more gently than weight does. Chemotherapy is the best-known example — most cytotoxic regimens are prescribed in mg/m², because the therapeutic window is narrow enough that dosing on weight alone would be too crude. Cardiac output is indexed to BSA as well, which is how you get the cardiac index, letting you compare a small patient and a large one meaningfully. Some paediatric doses and burn calculations use it too.
A practical note on formulas: Mosteller is the one used most often at the bedside because you can do it on any calculator with a square root button. Du Bois and Haycock exist and give slightly different figures, and the difference between them is small enough to be clinically irrelevant in most situations — but not in chemotherapy, where the institution specifies which formula to use and everyone sticks to it. If you're checking a chemo dose, use the formula your protocol names, not the one you find first.
| Patient | Mosteller working | Mosteller | Du Bois |
|---|---|---|---|
| 170 cm, 70 kg | √(170 × 70 ÷ 3,600) = √3.306 | 1.82 m² | 1.81 m² |
| 158 cm, 52 kg | √(158 × 52 ÷ 3,600) = √2.282 | 1.51 m² | 1.51 m² |
| 185 cm, 95 kg | √(185 × 95 ÷ 3,600) = √4.882 | 2.21 m² | 2.19 m² |
| 120 cm, 23 kg | √(120 × 23 ÷ 3,600) = √0.767 | 0.88 m² | 0.88 m² |
The two formulas agree to within a few hundredths for typical adults and drift apart at the extremes of size, which is why a chemotherapy protocol names the formula it uses. Du Bois is BSA = 0.007184 × weight0.425 × height0.725, with weight in kg and height in cm. The calculator shows three decimals; the table rounds to two, as most protocols do.
With height in inches and weight in pounds, Mosteller becomes √(height × weight ÷ 3,131). A patient 5 ft 7 in (67 in) and 154 lb: 67 × 154 = 10,318, ÷ 3,131 = 3.295, square root = 1.82 m². That matches the metric answer for 170 cm and 70 kg to within rounding.
A dose prescribed in mg/m² is the BSA multiplied by the dose per square metre. For a fictional order of 100 mg/m² and a BSA of 1.82 m²: 100 × 1.82 = 182 mg. Use the rounded BSA your protocol specifies; rounding BSA to two decimals and then the dose to the nearest whole milligram is a common convention, but chemotherapy rounding rules are set locally and checked by a pharmacist.
The Mosteller formula (√[height × weight ÷ 3600]) is the most widely used in clinical practice due to its simplicity and accuracy. Other formulas exist (DuBois, Haycock, Gehan-George) but the differences are clinically insignificant in most contexts. Many oncology services use Mosteller, but the formula is set by the local protocol.
The average BSA for an adult female is approximately 1.6 m² and for an adult male approximately 1.9 m². Paediatric BSA ranges from about 0.25 m² in newborns to about 1.1 m² in a 10-year-old child.
1.82 m² using Mosteller. Multiply 170 × 70 = 11,900, divide by 3,600 = 3.31, then take the square root = 1.82 m².
Use the US form of the Mosteller formula: BSA = √(height in inches × weight in pounds ÷ 3,131). For 67 inches and 154 lb, 67 × 154 ÷ 3,131 = 3.295, and the square root is 1.82 m².