Body Fat Calculator
Estimate body fat percentage with the US Navy tape method (Hodgdon & Beckett, 1984) from height, neck and waist — hips for women.
US Navy circumference method (Hodgdon & Beckett, 1984): 495 / (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450 for men; women add the hip to the girth term and use the female coefficients (1.29579 / 0.35004 / 0.22100). Measure the neck below the larynx, the waist at the navel (men) or narrowest point (women), the hip at its fullest part.
This tool runs entirely in your browser. Your data never leaves your device — it is not uploaded to any server.
How to use
- 1Choose your sex and metric or imperial units.
- 2Measure and enter height, neck and waist — plus hip for women.
- 3Read your estimated body fat percentage.
- 4Re-measure monthly under the same conditions to track the trend.
Body Fat Calculator
The US Navy circumference method estimates body fat from a tape measure alone. For men: %BF = 495 / (1.0324 − 0.19077·log10(waist − neck) + 0.15456·log10(height)) − 450, all in centimeters. Women add the hip to the girth term — log10(waist + hip − neck) — and use the female coefficients of the same 1984 paper by Hodgdon and Beckett.
Measure the neck below the larynx with the tape sloping slightly down at the front, the waist at the navel for men or the narrowest point for women, and the hip at its fullest part. Keep the tape snug but not compressing the skin. The result is an estimate with a typical error of ±3–4% against lab methods, not a diagnosis.
Frequently asked questions
How accurate is the Navy method?
Against underwater weighing and DEXA, the 1984 Navy equations average within about 3–4 percentage points, with individual errors larger where fat is stored unusually. It tracks changes well when you measure consistently, which matters more for progress than the absolute number.
What body fat range is considered healthy?
The American Council on Exercise cites for men: 2–5% essential fat, 6–13% athletes, 14–17% fitness, 18–24% average, 25%+ obesity. For women: 10–13% essential, 14–20% athletes, 21–24% fitness, 25–31% average, 32%+ obesity. Women need more essential fat for hormone function.
Why did the result come out negative or impossible?
The formula is printed unclamped, so impossible inputs — for example a waist not larger than the neck — produce impossible outputs. Treat any value below essential-fat level or above ~60% as a measurement error and re-measure. And as always, this estimate is not medical advice.
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