How the US Navy method works
The US Navy formula estimates body fat from body circumferences rather than skinfolds. For men it uses height, neck, and waist; for women it adds hip circumference, because fat distribution differs by sex. The measurements feed a logarithmic equation that correlates circumference ratios with body density. Because it needs only a tape measure, it is one of the most practical at-home methods and is far more informative about composition than BMI alone.
Measuring accurately
Accuracy depends entirely on good measurements. Measure the neck just below the larynx, the waist at the navel for men and at the narrowest point for women, and the hip at its widest. Keep the tape snug but not compressing the skin, stand relaxed, and measure at the same time of day — ideally in the morning — for consistent tracking. A waist reading that is smaller than the neck will produce an error, since the formula depends on the waist being larger.
Reading your category
The tool maps your result to standard ACE fitness ranges. For men, essential fat is 2–5%, athletes 6–13%, fitness 14–17%, average 18–24%, and obese 25%+. For women, the bands are higher — essential 10–13%, athletes 14–20%, fitness 21–24%, average 25–31%, obese 32%+ — because women carry more essential fat for hormonal and reproductive health. Some body fat is vital; dropping to essential levels is neither sustainable nor healthy long term.
A worked example
A man 175 cm tall with a 38 cm neck and 85 cm waist estimates around 18% body fat, landing at the boundary of the fitness and average ranges. Trim the waist to 80 cm and the estimate falls to roughly 15%, into the fitness range — illustrating how sensitive the result is to waist size, which is exactly why consistent tape technique matters more than any single reading.
Health disclaimer
This calculator provides general guidance only and is not medical advice. Tape estimates are typically within about 3–4% of laboratory methods like DEXA, but they remain approximations. For clinical assessment or if you have health concerns, consult a qualified healthcare provider who can use validated measurement tools.