Your weight on the scale doesn't show what it's made of. Two people of the same height and weight can have very different amounts of fat and muscle. This free body fat calculator estimates your body fat percentage using the US Navy method, a formula developed for military fitness screening that needs nothing more than a tape measure. You enter your height and your neck and waist circumference, plus your hip circumference if you're a woman. The calculator then gives your estimated body fat percentage, your fat mass and lean mass if you add your weight, and the category your result falls into on the American Council on Exercise (ACE) scale, from essential fat through athletes, fitness and average to obese. It works in centimetres or inches. To get consistent readings, measure the waist at the navel for men and at the narrowest point for women, measure the neck just below the larynx, keep the tape level and snug without compressing the skin, and measure at the same time of day each time. Tape methods are typically within about 3% to 4% of lab measurements such as DEXA, so track the trend over weeks rather than chasing a single number. This is for information only and isn't medical advice.
Calculate body fat
How to measure
- Neck: just below the Adam’s apple, tape sloping slightly down at the front.
- Waist: at the navel (men) or the narrowest point (women), relaxed, not sucked in.
- Hips (women): at the widest point of the buttocks.
ACE body fat categories
| Category | Women | Men |
|---|---|---|
| Essential fat | 10–13% | 2–5% |
| Athletes | 14–20% | 6–13% |
| Fitness | 21–24% | 14–17% |
| Average | 25–31% | 18–24% |
| Obese | 32%+ | 25%+ |
FAQ
How accurate is the US Navy method?
Usually within about 3–4 percentage points of lab methods, provided you measure carefully and consistently.
Why do women need a hip measurement?
The women’s formula uses waist plus hips minus neck, reflecting typical differences in fat distribution.
Is body fat better than BMI?
It tells you more about body composition. BMI is simpler; using both gives a fuller picture.
Is my data stored?
No. Everything is calculated in your browser.
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