Body Surface Area (BSA) Calculator

Calculator

How we calculate it

Body surface area is estimated rather than measured, and several published equations exist. This calculator reports four of them: Mosteller (1987), the square root of height in centimeters multiplied by weight in kilograms divided by 3600; Du Bois and Du Bois (1916), 0.007184 × height^0.725 × weight^0.425; Haycock (1978), 0.024265 × height^0.3964 × weight^0.5378; and Gehan and George (1970), 0.0235 × height^0.42246 × weight^0.51456. Mosteller is reported as the primary value because it is the form most widely used in practice and simple enough to verify by hand. The others are shown deliberately rather than hidden, together with the spread between the highest and lowest, because that spread is the most honest available indication of how precisely a single BSA figure can be read — published comparisons find the formulas agree closely at average body size and diverge meaningfully at higher body weight. BSA matters clinically because drug doses, particularly in oncology, and indexed measurements such as eGFR in mL/min/1.73m² are scaled to it. Where a protocol names a specific equation, that equation is the one that applies; they are not interchangeable.

Important limitations

• Every BSA equation is a regression fitted to a small measured sample — Du Bois and Du Bois used nine subjects — so all of them are approximations and they disagree with one another at the same height and weight.
• BSA is used clinically to scale drug doses and index measurements. Choosing a dose from a BSA figure is a clinical decision that depends on the drug and the protocol, and this calculator is for understanding the number rather than for dosing.
• The equations were derived in adults of average build and are least reliable at the extremes — in infants, in very short or very tall people, and at very high body weight, where some protocols cap or adjust the calculated value.
• BSA takes no account of body composition. Two people of the same height and weight get the same figure whether that weight is mostly muscle or mostly fat.
• Amputation, significant edema and pregnancy all change the relationship between height, weight and true surface area in ways these equations do not model.
• BSA is a scaling quantity rather than a measure of health, and it carries no interpretation about a person on its own.