Estimate body fat % using the US Navy (Hodgdon-Beckett) circumference method.
A free, in-browser body fat percentage estimator using the US Navy (Hodgdon-Beckett) circumference method. Enter your height, neck, and waist — plus hip if female — and get an instant estimate with the American Council on Exercise classification (Essential, Athletes, Fitness, Average, Obese). The method was developed from Navy personnel measurements and is a reasonable alternative when calipers, DEXA, or hydrostatic weighing aren't available. All calculation happens locally in your browser; your measurements are never uploaded.
Select your sex
The formula is different for male and female, and the female version also requires a hip measurement.
Measure and enter height
Metric (cm) or imperial (feet + inches). Stand against a wall without shoes.
Measure your neck, waist, (and hip)
Use a flexible tape measure. Neck: just below the Adam's apple, horizontal. Waist: at the navel for male, narrowest point for female. Hip (female): widest point of hips and buttocks. Keep the tape horizontal and snug but not compressing.
Read your body fat percentage
The result updates live along with the ACE fitness category. Remeasure on the same day of the week under similar conditions to track changes.
It's reasonably accurate for a typical adult — within about ±3% body fat compared to hydrostatic weighing in the original Navy validation study. It's less accurate at the extremes: very lean, very muscular, or very obese bodies tend to read off. For a clinical-grade number, DEXA or BodPod is the gold standard.
Female fat distribution is more gluteo-femoral, so the neck-and-waist difference alone doesn't capture it. Adding hip circumference gives the formula enough information to estimate total fat accurately.
Neck: just below the Adam's apple (larynx), tape horizontal, relaxed. Waist: at the navel for male, or at the narrowest point between ribs and hips for female. Hip: at the widest part of the hips and buttocks. Keep the tape snug against the skin but don't compress. Measure on bare skin or over a thin layer only.
The ACE fitness category is a good starting point: for male, 14–17% is 'Fitness' and 18–24% is 'Average'; for female, 21–24% is 'Fitness' and 25–31% is 'Average'. Below the essential-fat threshold (≈6% male, ≈14% female) is associated with health risks.
No. Every calculation runs in your browser. Your measurements and the computed body-fat value are never sent to a server.
The US Navy body-fat method was derived by Hodgdon and Beckett (Naval Health Research Center, 1984) from multiple-regression analysis of circumferences against hydrostatic weighing in approximately 600 Navy personnel. The male equation uses abdominal (waist) circumference minus neck circumference as the primary predictor, with height as an adjuster; the female equation adds hip circumference to account for gluteo-femoral fat distribution. Both equations apply the Siri/Brozek conversion (495/density − 450) to translate body density into percent fat. Validation studies since the 1980s have shown the method is within about ±3% body fat versus hydrostatic weighing in typical adults, with larger errors at the extremes of body composition. The ACE fitness categories (Essential, Athletes, Fitness, Average, Obese) are widely used in fitness settings but are not diagnostic — they are population-derived bands, not individual targets.