The US Navy body fat formula estimates body fat percentage from height and circumference measurements. Unlike skinfold calipers or DEXA scans, it requires only a tape measure — making it a practical field method used by the US military for fitness assessment. Accuracy is ±3–4% compared to DEXA, which is clinically acceptable for tracking trends over time.
For men: 495 / (1.0324 − 0.19077 × log10(waist − neck) + 0.15456 × log10(height)) − 450. For women: 495 / (1.29579 − 0.35004 × log10(waist + hip − neck) + 0.22100 × log10(height)) − 450. All measurements in centimetres. The logarithmic transformation accounts for the non-linear relationship between circumference measurements and body composition at different body sizes.
Compared to the gold standard (DEXA scan), the Navy formula has a mean error of about ±3–4 percentage points. It is less accurate at very low or very high body fat levels, but reliable for tracking change over time.
Waist: at the narrowest point (usually just above the navel). Neck: below the larynx (Adam's apple), perpendicular to the spine. Hip (women only): at the widest point. Measure without compressing the skin.
American Council on Exercise categories: Essential fat is 2–5% (men) / 10–13% (women). Athlete: 6–13% / 14–20%. Fitness: 14–17% / 21–24%. Average: 18–24% / 25–31%. Obese: 25%+ / 32%+.
Body fat percentage is a more direct measure of adiposity than BMI, which can't distinguish muscle from fat. However, both are proxies — neither equals a direct clinical measurement like DEXA.
See also the BMI Calculator and BMR Calculator for a complete health metrics picture.