Body Fat Calculator (Navy Method)
US Navy circumference method: uses tape measurements of neck, waist (and hip, for women) to estimate body fat. Accuracy is roughly ±3–4% vs. clinical DEXA. Better than BMI as an individual metric, less accurate than DEXA or hydrostatic weighing.
Estimated Body Fat
Reference Ranges (ACE, general adult)
How the Navy method works
The US Navy developed this formula in the 1980s as a low-cost body fat screening for military members. It uses circumference measurements at specific anatomical points to estimate body density, then converts to body fat percentage via the Siri equation.
Men: 86.010 × log₁₀(waist − neck) − 70.041 × log₁₀(height) + 36.76
Women: 163.205 × log₁₀(waist + hip − neck) − 97.684 × log₁₀(height) − 78.387
The formula predicts subcutaneous fat well; it's less accurate for people with atypical fat distribution (visceral fat, extremes of body composition). It works better for the middle of the population than for very lean athletes or people with high body fat, where DEXA or hydrostatic weighing become more reliable.
ACE reference ranges (adult, general population)
These are population reference ranges from the American Council on Exercise, not health prescriptions. Optimal body fat varies with individual goals, activity, and stage of life. Very low body fat is not a health target for most people.
Measurement tips
Measure first thing in the morning, before eating or drinking. Neck: just below the larynx, tape level, looking forward. Waist (men): at the navel level, tape horizontal, breathe normally. Waist (women): narrowest point between ribs and hips. Hip (women): widest circumference of the hips/glutes. Do 3 measurements each and use the average.