Body surface area calculation using the simplified Mosteller formula.

What it is and when to use it

This body surface area calculator applies the Mosteller formula, BSA (m²) = √(height in cm × weight in kg / 3600), and rounds the result to two decimal places. R. D. Mosteller published it in 1987 in a letter to the New England Journal of Medicine entitled 'Simplified calculation of body-surface area': height, weight and a square root are all it takes. BSA in m² is the body-size measure in which many cytotoxic doses are expressed (mg/m²); it is also used to derive cardiac index and to index glomerular filtration rate. The page accepts values from 10 cm and 0.5 kg up to 250 cm and 300 kg, including paediatric measurements.

How to interpret it

The result is an area in m², which the page places in one of three bands: below 1.4 m², under the usual adult range, as in children and small adults; 1.4 to 2.2 m², the standard adult range; and above 2.2 m², as in tall people or those with obesity. The default values (170 cm, 70 kg) give 1.82 m²; a child of 110 cm and 18 kg has 0.74 m², and an adult of 190 cm and 110 kg has 2.41 m². Because height and weight sit under a square root, doubling the weight does not double the surface area.

Limitations and when not to use it

The formula needs height in centimetres and weight in kilograms; a weight entered in pounds usually falls within the limits the page accepts, so the error can go unnoticed. Marked oedema, ascites or an amputation can pull weight away from true body size. Mosteller is not the only equation (the DuBois and DuBois formula is still in use) and the methods do not agree exactly, so use whichever the protocol specifies. The calculator applies no cap to BSA; in obesity, whether a dose is capped is decided by each drug's protocol.

Frequently asked questions

How do you calculate body surface area with the Mosteller formula?

Multiply height in centimetres by weight in kilograms, divide by 3600 and take the square root. For 170 cm and 70 kg: 170 × 70 = 11,900; 11,900 / 3600 = 3.31; √3.31 = 1.82 m². Convert a height recorded in metres to centimetres first.

How is body surface area used in chemotherapy?

Many cytotoxic drugs are prescribed in mg per m²: the patient's dose is the regimen's per-m² dose multiplied by their BSA. This page calculates only the BSA; the final dose and any cap are set by the protocol.

What is a normal body surface area for an adult?

The page treats 1.4 to 2.2 m² as the standard adult range. There is no 'healthy' or 'unhealthy' BSA: it is a measure of size, useful for scaling doses or indexing other parameters, not for classifying the patient.

Should body surface area be recalculated if weight changes?

Yes, because the formula uses current weight, although the square root dampens the effect: losing 10% of body weight lowers BSA by about 5% (at 170 cm, going from 70 to 63 kg takes it from 1.82 to 1.72 m²).