Body Fat Calculator
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Estimate your body fat percentage using the US Navy circumference method. Enter a few tape measurements in metric or imperial units and see your result and fitness category, all calculated on your device.
How the US Navy method works
This calculator uses the US Navy circumference method, a tape-measure technique developed to estimate body composition without calipers or lab equipment. It relies on the fact that fat and lean tissue distribute differently around the neck, waist and hips, so those circumferences (combined with height) predict body fat reasonably well for most people.
For men the formula is 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450. For women it adds the hip measurement: 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.22100 x log10(height)) - 450. All measurements are converted to centimetres internally, so imperial input works too.
Measuring accurately
The result is only as good as your tape work, so consistency matters more than anything. Use a flexible, non-stretch tape held level and snug against the skin without compressing it, and take each measurement two or three times to average out small errors.
Standard landmarks help: measure the neck just below the larynx sloping slightly downward at the front, the waist at the navel for men or the narrowest point for women, and the hips at the widest part of the buttocks. Measuring at the same time of day under the same conditions makes comparisons over time far more meaningful.
- Neck: just below the Adam's apple, tape sloping down to the front
- Waist (men): horizontally at the navel
- Waist (women): at the narrowest point of the torso
- Hip (women): at the widest point of the buttocks
Reading your category
The percentage is grouped into categories based on the American Council on Exercise ranges, which differ by sex because women naturally carry more essential fat. For men, essential fat sits around 2 to 5 percent, athletes 6 to 13, fitness 14 to 17, average 18 to 24 and obese at 25 or above. For women the same bands are roughly 10 to 13, 14 to 20, 21 to 24, 25 to 31 and 32 or above.
Treat the number as an estimate rather than a lab reading. The Navy method is convenient and repeatable, but methods like DEXA or hydrostatic weighing are more precise. For most people the real value is watching the trend over weeks, not obsessing over a single decimal.
Frequently asked questions
Why do women need a hip measurement but men do not?
Women store more fat around the hips, so the female formula includes the hip circumference to capture that distribution and improve the estimate. The male formula relies on neck and waist alone.
How accurate is the Navy method?
For most people it lands within a few percent of lab methods, but accuracy depends heavily on measuring carefully. It tends to be less reliable at the extremes of very lean or very high body fat.
Why must my waist be larger than my neck?
The formula takes the logarithm of the waist-minus-neck value, which must be positive. If your entries give a zero or negative difference, the measurements likely need rechecking.
What is a healthy body fat percentage?
It varies by age and sex, but a common healthy range is roughly 14 to 24 percent for men and 21 to 31 percent for women. Athletes are often lower, and essential fat should not be dropped below safe minimums.
How often should I remeasure?
Every two to four weeks is enough to see a real trend. Measuring under the same conditions each time, such as first thing in the morning, reduces noise from food, water and time of day.
Are my measurements saved?
No. Everything is computed locally in your browser, so your neck, waist, hip and height figures never leave your device.
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