Body Surface Area Calculator
Du Bois, Mosteller, Haycock and Boyd side by side.
Body Surface Area Calculator works out BSA from height and weight using the Du Bois, Mosteller, Haycock and Boyd formulas at once, so you can see how far they disagree. It can also index a dose per square metre or a cardiac output. The figures never leave your browser.
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Runs entirely on your device. No file or text you enter here is uploaded. How to verify it.
This is a calculation tool, not medical advice. The result is an estimate from a published formula and cannot account for your individual circumstances. Talk to a healthcare professional about anything that matters.
How to use Body Surface Area Calculator
- Choose metric or imperial and enter height and weight.
- Compare the four formulas and the spread between them.
- Optionally add a dose per square metre or a cardiac output to index.
Questions about Body Surface Area Calculator
Which formula should I use?
Mosteller, in most clinical settings, for the plainest of reasons: it is a single square root, so it can be done at a bedside and checked by a second person without a computer. Haycock is the usual choice in paediatrics because children were in its sample. What matters more is using the one your protocol names.
How much do they disagree?
Very little at an average adult build — a few tenths of a percent at 175 cm and 70 kg — and much more at the extremes, around 6% at 190 cm and 150 kg, and over 10% for an infant. That is because each equation is a fit to a small sample: Du Bois used nine people in 1916, and none of the originals included many obese adults.
Is BSA a fitness or body-composition measure?
No. It says nothing about health, fat, or how fit anyone is. It exists because some things in medicine scale with surface area rather than mass: chemotherapy and certain other doses, cardiac index, glomerular filtration rate normalised to 1.73 m², and burn assessment.
Why do some protocols cap BSA at 2 m²?
Because the formulas were never fitted over that range, so an extrapolated area for a very large patient carries real uncertainty, and the dose that follows from it may exceed what is safe. Capping is a deliberate clinical decision made in the protocol, not a property of the arithmetic.
Can I use this to work out a dose?
No. The dosing box is there to show how much the choice of formula alone moves a result, which is the point worth taking away. Doses are set by prescribers against a protocol, with checks this page cannot perform, and nothing here should be used to set or change one.
Is Body Surface Area Calculator really free, with no limits?
Yes. There is no account, no daily cap, no file-size tier and no watermark, because there is no server cost to recover. The site is funded by clearly disclosed partner recommendations on the Partners page, never by metering the tools.
Are my files or text uploaded when I use Body Surface Area Calculator?
No. Everything is processed by JavaScript running in your browser, on your device. You can verify it: open your browser's developer tools, switch to the Network tab, and use the tool. You will see no request carrying your data — because there is nowhere for it to go.