The U.S. Navy body fat formula estimates body fat percentage from simple tape measurements of your neck, waist, and hip circumference. Enter your measurements and height to get an estimate along with the body fat category for your gender.
Body fat percentage is the proportion of your total body weight that comes from fat tissue, as opposed to lean tissue (muscle, bone, water, organs). It's a more nuanced measure of body composition than weight or BMI — a 200-pound lifter with 12% body fat is in a very different fitness category than a 200-pound sedentary person with 30% body fat, even though their scale weight and BMI may be similar.
The U.S. Navy developed this circumference-based formula in the 1980s as a practical way to estimate body fat without specialized equipment. It uses simple tape measurements of neck, waist, and (for women) hip circumference along with height. The Navy formula's big advantage is accessibility — anyone with a tape measure can use it. Its disadvantage is that it's an estimate, not a measurement: it assumes typical body fat distribution and can be off by 3–4% in either direction for individual results.
This calculator implements the Navy method to give you an estimate plus the standard fitness category for your gender. For more precise measurement, the gold standards are DEXA scans (best, but expensive at $50–$150 per scan), hydrostatic underwater weighing (very accurate but rare equipment), Bod Pod air displacement, or skinfold calipers (cheap but requires skill). Bioimpedance scales and handheld devices are popular but generally less accurate than the Navy tape method for most people.
30-year-old man, 5'10" (70 inches), 32-inch waist, 15-inch neck, 165 lbs. log₁₀(32 − 15) = log₁₀(17) = 1.230 log₁₀(70) = 1.845 Body Fat % = 86.010 × 1.230 − 70.041 × 1.845 + 36.76 ≈ 105.8 − 129.2 + 36.76 ≈ 13.4% Fat mass: ≈ 22 lbs. Lean mass: ≈ 143 lbs. Category: Athletes range (6–13%) — just above. Very good body composition.
40-year-old woman, 5'5" (65 inches), 30-inch waist, 13-inch neck, 39-inch hip, 145 lbs. log₁₀(30 + 39 − 13) = log₁₀(56) = 1.748 log₁₀(65) = 1.813 Body Fat % = 163.205 × 1.748 − 97.684 × 1.813 − 78.387 ≈ 285.3 − 177.1 − 78.4 ≈ 29.8% Fat mass: ≈ 43 lbs. Lean mass: ≈ 102 lbs. Category: Acceptable for women (25–31%). Above "Fitness" range (21–24%); below "Obese" threshold (32%+).
Two men, both 5'10" tall and weighing 190 lbs. BMI = 27.3 for both (categorized as "Overweight"). Man A (lifter): 36-inch waist, 16-inch neck. Body Fat ≈ 17%. Man B (sedentary): 40-inch waist, 16-inch neck. Body Fat ≈ 26%. Same BMI category, vastly different composition. Man A has ~32 lbs of fat and 158 lbs of lean mass — "fitness" range and quite muscular. Man B has ~49 lbs of fat and 141 lbs of lean mass — into obese range. This is exactly why body fat percentage is more meaningful than BMI for assessing real fitness — BMI can't tell the difference between high muscle mass and high body fat.
Use this calculator when starting or tracking a body recomposition program, when curious about your current body composition, or when BMI categorization doesn't match your sense of your own fitness. It's also useful for athletic populations where BMI can be misleading (lifters, athletes, anyone with significant muscle mass).
For weight loss progress, body fat percentage is often a more meaningful metric than the scale. A successful resistance-training-plus-nutrition program may show only modest weight loss on the scale while body fat percentage drops significantly (you're losing fat and gaining muscle simultaneously). The scale doesn't capture this; body fat percentage does.
Pair this with the BMI calculator (the simpler weight-only measure), the BMR/TDEE calculators (calorie needs based on lean mass and activity), the ideal-weight calculator (target weight estimation), and the calorie/macro calculators (the deficit/surplus tools).
A practical note on accuracy: the Navy formula is best for individuals with reasonably typical fat distribution. People who carry weight unusually (very narrow hips, very broad hips, large bust, etc.) will get less accurate estimates. For more precise tracking, DEXA scans every 6–12 months provide objective benchmarks; the Navy tape method is good for in-between progress tracking.
Body fat percentage isn't the only health metric. Waist-to-height ratio (waist circumference divided by height) is another useful measure, with a target of under 0.5 generally considered healthy regardless of body fat percentage. Visceral fat (deep abdominal fat) carries more health risk than subcutaneous fat (under the skin) — the waist circumference number itself is a useful proxy for visceral fat risk, especially above 40 inches for men or 35 inches for women.
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Body Fat %
18.3%
Category
Average
Fat Mass
31.1 lbs
Lean Mass
138.9 lbs