Body Fat Calculator
US Navy and BMI-based estimates, with their error range.
Body Fat Calculator estimates body fat percentage from tape measurements using the US Navy circumference method, and from height and weight using the BMI-derived Deurenberg equation. It reports both, along with lean mass, and states the accuracy range honestly. Measurements stay in 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 Fat Calculator
- Choose the Navy method or the BMI-based method.
- Enter the measurements it asks for.
- Read the estimate, the lean mass, and the accuracy note.
Questions about Body Fat Calculator
How accurate are these estimates?
The US Navy method sits within roughly ±3-4 percentage points of a DEXA scan for most people, and worse at the extremes of body composition. The BMI-derived equation is cruder still. Both are useful for tracking a trend over months; neither is a measurement.
Which measurements does the Navy method need?
Height, neck and waist for men; height, neck, waist and hips for women. Measure at the same points and at the same time of day each time, since a centimetre of tape error moves the result by more than a percentage point.
Is there a healthy body fat range?
Reference ranges exist and are shown, but they vary by age, sex and athletic status, and body fat percentage on its own says little about health. This is a calculation tool, not an assessment.
How does this compare with callipers or a smart scale?
Skinfold callipers in practised hands are usually a little tighter than the tape method. Bioimpedance scales swing with hydration and can read several points apart between morning and evening. All three are estimates; DEXA is the practical reference, and that is a clinic appointment rather than a web page.
Are my measurements sent anywhere?
No. Waist, neck and hip measurements are personal data, and they stay in the tab — nothing is uploaded, logged or written to storage. Closing the page discards them, and there is no account to attach them to in the first place.
Is Body Fat 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 Fat 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.