U.S. Navy Body Fat Calculator
Estimate body fat percentage from neck, waist (and hip) circumference using the U.S. Navy circumference method, in metric (cm) or imperial (in) units.
- Body fat %
- 10.8
- Category
- Athletes
Where this falls
10.8 falls in the "Athletes" range.
How it works
This is the U.S. Navy circumference method (Hodgdon & Beckett, 1984), the formula the Navy actually uses for body composition screening in place of skinfold calipers. It estimates body density from a log-linear regression on a few tape-measure circumferences, then converts density to a body fat percentage with the Siri equation: %BF = 495 ÷ density − 450.
For men, body density = 1.0324 − 0.19077·log₁₀(waist − neck) + 0.15456·log₁₀(height). For women, who carry fat differently, hip circumference is added: body density = 1.29579 − 0.35004·log₁₀(waist + hip − neck) + 0.22100·log₁₀(height). These published coefficients are calibrated for inches, so metric (cm) entries are converted to inches before the formula runs and back afterward — the result is identical either way.
The category bands shown (Essential fat, Athletes, Fitness, Acceptable, Obese) are the standard American Council on Exercise ranges, which differ by sex since essential fat is higher for women.
FAQ
How accurate is the tape-measure method compared to other body fat tests?
It's less precise than a DEXA scan or hydrostatic weighing, but it's a well-validated field method — the U.S. military has used it for decades because it only needs a tape measure and gives a reasonably consistent estimate. Measurement technique matters: measure at the same spot, snug but not compressed, for a repeatable number.
Where exactly should I measure my waist and neck?
The Navy method measures the neck just below the larynx, and the waist at the navel for men or at the narrowest point (or navel, per the original protocol) for women; hip is measured at the widest point around the buttocks. Precise, consistent placement matters more for this formula than for a casual estimate, since it's fairly sensitive to the circumference differences.