What does this tool do?
This tool estimates your body fat percentage from just a few tape-measure circumferences using the US Navy method. Men enter height, waist, and neck; women add a hip measurement. The result is also placed into a category — essential, athlete, fitness, average, or obese — for quick context.
How to use it
- Enter your values into the fields.
- The result is calculated instantly.
- Read or copy the result.
How the US Navy method works
The method feeds your tape measurements into a logarithmic formula. For men it uses the difference between waist and neck plus height; for women it uses waist plus hip minus neck, along with height. Measure against bare or thin clothing without pulling the tape tight: take the waist at navel level and the neck just below the larynx. The percentage is shown with a color-coded category, so you can instantly see whether you fall in the athlete or average range.
Tips for an accurate measurement
For consistency, always measure at the same time of day, ideally in the morning before eating. Keep the tape snug but not compressing the skin, and parallel to the floor. Rather than relying on a single reading, measure over a few days and average the results. Even a half-centimetre difference can shift the outcome, so having the same person measure each time improves reliability.
Frequently asked questions
Which measurements do I need to enter?
Men enter height, waist, and neck; women add hip. You can choose centimetres or inches with the unit toggle.
How accurate is the US Navy method?
It is a circumference-based estimate, often close to caliper readings, but can differ by a few points from clinical methods like DEXA.
Why does it show 'Invalid input'?
If the waist and neck values are inconsistent — for example a neck larger than the waist — the formula cannot produce a valid number, so recheck your measurements.
Is Body Fat Calculator free?
Yes. Body Fat Calculator and all 300+ tools on MagmaNex are completely free with no signup or account required.
Is my data safe?
Yes. Everything runs locally in your browser. The data you enter is never sent to a server, stored, or shared.
Does it work on mobile?
Yes. Body Fat Calculator works on phones, tablets and desktops — no app download needed.
🔒 Privacy: everything runs in your browser, your data is never sent to a server.