Body surface area calculator with Mosteller and Du Bois methods
Calculate body surface area
Body surface area calculator: methods, accuracy, and when BSA helps
Body surface area is a scaled measure of body size that often tracks physiological needs better than weight alone. Many clinical workflows reference BSA for dose bands, fluid plans, or cardiac index. This page focuses on two practical methods that you can compute with basic inputs: the Mosteller square-root shortcut and the Du Bois allometric equation. Both draw on height and weight and both return results in square meters, the convention in clinical practice.
The Mosteller shortcut multiplies height in centimeters by weight in kilograms, divides by 3600, and takes a square root. Its appeal is clarity: anyone can audit the steps and spot a swapped digit. Du Bois uses fractional exponents on height and weight to match observed patterns across different body sizes. In typical adult ranges the outputs are close; if you see a large gap, it usually means an input error rather than a meaningful physiologic difference.
Because many visitors think in feet, inches, and pounds, the calculator accepts US entries and echoes your numbers in both systems. Your results appear in square meters and square feet so the scale is intuitive without changing the underlying calculation. For example, a reading near 1.9 m² corresponds to roughly 20.5 ft². This dual display helps with communication while keeping the method consistent with clinical conventions.
BSA is useful but not definitive. Providers also weigh kidney and liver function, age, drug interactions, and lab values. Edema, pregnancy, or rapid fluid shifts can change weight without reflecting true tissue size, which makes height–weight formulas less representative. In those settings teams may prefer dosing protocols that cap or adjust BSA, or they may reference additional markers such as lean mass or allometric scaling tailored to the drug.
When you use this calculator, aim for clean inputs. Measure height without shoes and avoid rounding too aggressively; half-centimeter accuracy is fine. Weigh yourself on a flat surface at a similar time of day, preferably in the morning. If you enter US units, the tool converts internally to centimeters and kilograms before applying the formulas. The result box shows both methods, a note on how closely they agree, and a reminder that the page is informational rather than medical advice.
For follow-ups, pick one equation and stick with it so your numbers remain comparable over time. If your clinic or protocol specifies a particular method and rounding rule, use that consistently. If anything looks off—such as a BSA that jumps markedly between days—recheck your height and weight entries and verify unit symbols. Small entry errors can shift the result more than expected, especially with decimal points or mixed-unit confusion.
Body surface area calculator FAQs
Which equation should I choose?
Use the method your clinic or protocol specifies. Mosteller is common for its simplicity; Du Bois is also accepted. Be consistent across visits.
Why show m² and ft²?
Clinicians chart in m², but many US users think in feet and inches. Displaying both keeps results understandable without changing the math.
How close are the two results?
Usually within about 0.05 m² for adult sizes. Big differences often indicate a data entry or unit error.
Can I use this to change a dose?
No. This page is informational only. Never adjust medication without a prescriber’s guidance.