General
Body Surface Area (Mosteller)
BSA from height and weight.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
Body surface area (BSA) is an estimate of the total external surface of the body, used to index drug doses and physiological measurements that scale better with surface area than with weight alone. The Mosteller formula is the most widely used because of its simplicity: BSA (m²) = the square root of (height in cm × weight in kg / 3600). It is applied in oncology (chemotherapy dosing), cardiology (cardiac index) and other settings where dosing or physiology is normalised to body size. The result is expressed in square metres.
Interpreting the result
A typical adult BSA is around 1.7–2.0 m², with most chemotherapy and physiological reference values assuming roughly 1.7–1.8 m². There is no normal or abnormal range as such; the value is simply used as a denominator or multiplier in downstream calculations. Because it is derived from height and weight, accuracy depends entirely on accurate measurement of both, and extremes of body habitus reduce its reliability.
Worked example
For a patient who is 170 cm tall and weighs 70 kg: BSA = √((170 × 70) / 3600) = √(11900 / 3600) = √3.31 ≈ 1.82 m². This value would then be used to index, for example, a surface-area-based calculation.
Pearls / pitfalls
- Different BSA formulae (Mosteller, Du Bois, Haycock) give slightly different values — use the one specified by the local protocol for consistency.
- BSA-based dosing is less reliable at extremes of body weight, particularly in obesity, where many centres cap or adjust the dose.
- Accurate, measured height and weight are essential; estimated values can introduce clinically important dosing errors.
- BSA is a sizing tool, not a clinical measurement — it has no normal range and should never be interpreted as a result in its own right.
Evidence & validation
The Mosteller formula was published as a simplified alternative to earlier, more complex equations and shown to agree closely with them. It is the formula most commonly recommended in clinical practice, including in many chemotherapy dosing protocols.
Frequently asked questions
Which BSA formula should I use?
Mosteller is the most widely used because it is simple and accurate enough for most purposes. However, you should use whichever formula your local protocol specifies, as small differences between formulae can change a calculated dose.
What is a normal body surface area?
A typical adult BSA is around 1.7–2.0 m². BSA is not a clinical measurement with a normal range; it is simply used to index doses and physiological values to body size.
Is BSA reliable in obesity?
Less so. BSA-based dosing can become unreliable at extremes of body weight, and many centres cap or adjust BSA-based doses in obese patients. Always follow local dosing guidance in these situations.
Why is BSA used instead of weight for some doses?
Some drugs and physiological measures (such as cardiac index) correlate better with surface area than with weight alone. Indexing to BSA aims to give more consistent values across people of different sizes.
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.
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