Body Surface Area Calculator
Calculate Body Surface Area (BSA)
Body Surface Area Calculator tool
Body Surface Area Calculator
Body Surface Area Calculator: key facts
- What it does
- Calculate Body Surface Area (BSA)
- Category
- Health & Fitness Calculators
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
Understanding the Body Surface Area Calculator
Body surface area is a measure clinicians rely on for things like medication dosing and assessing metabolic needs, because it reflects body size better than weight alone. This calculator computes it from your weight and height using the two most established equations — DuBois and Mosteller — side by side.
Healthcare students and professionals use BSA where precise body-size scaling matters, such as chemotherapy dosing or estimating cardiac index. Showing both formulas lets you cross-check, since they can differ slightly, and gives confidence in the figure you carry forward. Students working through pharmacology or physiology exercises also find the side-by-side output useful for understanding why textbooks and references sometimes quote marginally different BSA values for the same patient.
Getting a result
- Enter your weight in kilograms.
- Enter your height in centimeters.
- Read the DuBois body surface area result in square meters.
- Compare it against the Mosteller result shown alongside.
Du Bois and Mosteller, side by side
Body surface area is used clinically because several physiological quantities scale better with surface area than with weight — cardiac output, glomerular filtration rate, and most notably chemotherapy dosing, which is conventionally prescribed per square metre.
The tool reports two equations rather than one. Du Bois and Du Bois, from 1916, is the oldest in continuing use and applies fractional exponents to weight and height separately. Mosteller's, published in 1987, is a square root of the product divided by 3600 — simple enough to do on any calculator, which is precisely why it became the clinical default.
They agree closely across normal adult ranges, typically within a couple of percent, and showing both makes that agreement visible. Where they diverge is at the extremes of body size, and Du Bois is generally considered less reliable for very small or very large bodies.
- The default entry — 70 kg, 175 cm — gives 1.85 m² by Du Bois and 1.84 m² by Mosteller.
- Typical adult values run from about 1.6 m² to 2.0 m², so a difference of 0.01 m² between the two methods is immaterial for most purposes.
- A drug dosed at 350 mg/m² would therefore be prescribed at roughly 646 mg for this person — which shows why even small differences in BSA get scrutinised in oncology.
Reasons to use it here
- It computes both the DuBois and Mosteller formulas at once, letting you compare the two standard methods rather than trusting one.
- It reports results in square meters to two decimals, the precision clinical use expects.
- It needs only weight and height, the inputs both formulas use, keeping it simple.
- All math runs locally in your browser, so the figures stay private.
A note on clinical use
This calculator exists to check arithmetic, and that is the whole of its intended purpose. It is genuinely useful for confirming a figure you have already derived, for teaching, or for understanding a number that appears on a chart. It is not a dosing tool.
Real dose calculation involves considerably more than surface area: renal and hepatic function, prior treatment, current blood counts, capping conventions for very large body sizes, protocol-specific adjustments, and institutional policy on which BSA formula to use — hospitals differ, and using a different equation from the prescribing protocol introduces exactly the kind of discrepancy that dosing checks exist to catch.
Any dose administered to a patient must come from the responsible clinician working within their local protocol, with independent verification. Nothing on this page should be used to calculate, adjust, or check a dose for administration.
Frequently Asked Questions
What is body surface area used for?
BSA is used in medicine to scale things to body size — most notably dosing certain medications such as chemotherapy, and computing indices like cardiac output relative to body size. It often tracks physiological needs better than body weight alone.
What is the difference between the DuBois and Mosteller formulas?
Both estimate BSA from height and weight but use different equations — DuBois employs exponents on height and weight, while Mosteller uses a simpler square-root formula. They usually agree closely; showing both lets you verify the estimate.
Which BSA formula should I use?
Mosteller is popular for its simplicity and is widely used in clinical dosing, while DuBois is a long-standing standard. For most purposes they are interchangeable; follow whichever your institution or protocol specifies.
Does body surface area change if I gain or lose weight?
Yes. Because both weight and height feed the formulas, a change in weight shifts your BSA — though less dramatically than it shifts weight itself, since BSA grows slowly with size. Recalculate after a significant weight change if you are using BSA for dosing or metabolic estimates.
