Body Fat Calculator (US Navy Method)
Estimate body fat percentage from neck, waist (and hip) circumferences with the US Navy formula — plus your fitness category.
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Tape Measure Body Composition
The US Navy method estimates body fat from circumferences: for men it uses waist − neck and height; for women waist + hip − neck and height, in logarithmic formulas validated against underwater weighing (typical error ±3-4%). It beats BMI because it distinguishes a muscular 90 kg from a round one.
Measure right: waist at the navel (men) or narrowest point (women), relaxed — not sucked in; neck just below the larynx, tape sloping slightly down at the front; hip at the widest point. Categories (ACE): men — essential 2-5%, athletes 6-13%, fitness 14-17%, average 18-24%, obese 25%+; women run about 10 points higher across the board.
Frequently Asked Questions
How accurate is it versus a DEXA scan?
Typically within 3-4 percentage points — good for tracking trends monthly with consistent technique. DEXA and hydrostatic weighing are the reference standards for absolute numbers.
Why does my reading jump day to day?
Tape position and tension, bloating, and hydration all move centimeters. Measure the same time of day (morning, before eating), average two tapes, and watch the monthly trend.
What body fat should I aim for?
Health-wise, men ~10-20% and women ~18-28% cover most goals. Visible abs typically need ~10-12% (men) / ~16-19% (women) — and below essential fat is dangerous, not lean.
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Body Fat Calculator (US Navy Method)