Body surface area (Mosteller & Du Bois)

Calculate body surface area by the Mosteller equation, with the Du Bois equation shown for comparison.

High-consequence calculationBody surface area drives chemotherapy dosing, where small errors carry substantial consequences. Verify height and weight against the source record before use.

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What is this for?

Body surface area scales more closely with metabolic rate and cardiac output than weight does, which is why cytotoxic chemotherapy and several other narrow-therapeutic-index agents are dosed per square metre. Mosteller is the simplest and most widely used equation; Du Bois is the older reference standard and still appears in some protocols.

How to use it

Enter height in centimetres or inches.
Enter weight in kilograms or pounds. For chemotherapy, use the weight your protocol specifies — many use actual body weight, some use adjusted.
Use the Mosteller value unless the protocol names a different equation. Both are shown so you can see the magnitude of the difference.

Worked example

A patient is 170 cm and 70 kg. Calculate the body surface area for a chemotherapy dose.

Answer: (170 × 70) ÷ 3600 = 3.3056; √3.3056 = 1.82 m². Du Bois gives 1.81 m² — a 0.5% difference.

Clinical pearls & pitfalls

Independently verify the height and weight against the source record before calculating a cytotoxic dose. A transcription error in either propagates directly into the dose.
Different BSA equations give different answers, and the difference widens at the extremes of size. If a patient's dose is recalculated at a different institution using a different equation, expect a discrepancy — reconcile it rather than assuming an error.
BSA capping in obesity is now discouraged for most curative-intent chemotherapy: ASCO recommends using actual body weight to compute BSA, because capping led to underdosing and inferior outcomes. Follow the specific protocol.
Recalculate BSA when weight changes materially during a course of treatment, particularly with substantial fluid shifts or weight loss.

Assumptions & limitations

All BSA equations are regression estimates from small original samples — Du Bois used nine subjects. They are approximations, not measurements.
Validated primarily in adults of average build. Accuracy degrades in extreme obesity, in amputees, and in patients with major fluid overload.
BSA-based dosing itself is a rough surrogate for drug clearance and explains only a modest fraction of interpatient variability for many cytotoxics.

References

Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098.
Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17:863-871.
Griggs JJ, et al. Appropriate systemic therapy dosing for obese adult patients with cancer: ASCO guideline update. J Clin Oncol. 2021;39(18):2037-2048.