Body Fat Percentage Estimator
Estimate your body fat percentage using the U.S. Navy method with neck, waist, and hip measurements.
U.S. Navy Body Fat Method
The U.S. Navy method estimates body fat using circumference measurements. Males need neck and waist measurements; females also need hip measurement. While not as accurate as DEXA scans, it provides a reasonable estimate for tracking progress.
About This Tool
Estimates body fat percentage using the U.S. Navy circumference method. Inputs are height plus neck and waist circumference (men) or neck, waist, and hip (women). The formula was developed by Hodgdon and Beckett in 1984.
Accuracy is roughly ±3% compared with hydrostatic weighing for typical adult body shapes. Results outside the 5–40% range are increasingly unreliable.
The Hodgdon-Beckett equations were derived in a 1984 Naval Health Research Center study comparing tape measurements against hydrostatic weighing on US Navy personnel. Two separate formulas were validated: one for men using height, neck, and waist circumferences, and one for women adding hip circumference because female fat distribution loads more heavily on the hips and thighs. The equations log-transform the circumference measurements and combine them with constants fitted to minimize error against the gold-standard hydrostatic results.
A worked example: a 6-foot (72 inch) man with a 16-inch neck and 36-inch waist plugs into the male formula: %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. With waist − neck = 20 inches and height = 72 inches: 86.010 × log10(20) − 70.041 × log10(72) + 36.76 = 86.010 × 1.301 − 70.041 × 1.857 + 36.76 = 111.88 − 130.07 + 36.76 = 18.57%. This places the subject in the 'fitness' range for adult males.
Limitations are well-documented. The Navy method assumes typical adult body proportions; it loses accuracy for very lean athletes (where waist circumference is below the formula's calibrated range), heavily muscled individuals (where neck circumference inflates from muscle rather than fat), and very high body fat (where the relationship saturates). Hydrostatic weighing, DEXA scans, and BodPod air-displacement plethysmography are the validation references, with DEXA now considered the most accurate practical method. Skinfold caliper measurements with the Jackson-Pollock 7-site formula give similar accuracy to the Navy method when performed correctly. Bioelectrical impedance (handheld and scale-based) varies wildly with hydration and time of day; results from those should be treated as trend indicators rather than absolute values.
The healthy body fat ranges differ between men and women due to essential fat differences. For men: 6-13% athletes, 14-17% fitness, 18-24% average, 25%+ obese. For women: 14-20% athletes, 21-24% fitness, 25-31% average, 32%+ obese. Women carry more essential fat (12% vs. 3%) for reproductive function. These categories are general, not medical; specific health implications depend on overall body composition, fat distribution, and metabolic markers, not the percentage alone.
The about text and FAQ on this page were drafted with AI assistance and reviewed by a member of the Coherence Daddy team before publishing. See our Content Policy for editorial standards.