Free Body Fat Calculator
A tape measure beats a guess. Enter a few circumference measurements and get your body fat percentage with the US Navy formula.
This free body fat calculator uses the US Navy method, which estimates body fat from tape measurements instead of calipers or scans. Men enter height, neck, and waist; women add hips. A man with a 34-inch waist, 16-inch neck, and 70-inch height lands at 15.5 percent body fat, in the fitness range; a woman with a 28-inch waist, 38-inch hips, 13-inch neck, and 64-inch height lands at 26.6 percent, in the average range.
The Navy method estimates body fat within a few percentage points for most people; it is not as precise as a DEXA scan. Tape measurements must be snug but not compressing the skin.
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How the Navy body fat formula works
The US Navy method predicts body fat from circumferences because waist size tracks total fat and neck size tracks lean mass. For men: body fat percent = 86.010 x log10(waist - neck) - 70.041 x log10(height) + 36.76, all in inches. For women the formula adds hips: 163.205 x log10(waist + hip - neck) - 97.684 x log10(height) - 78.387.
Work the men's example: waist 34, neck 16, height 70. Waist minus neck is 18, and log10(18) is 1.2553, times 86.010 gives 108.0. Log10(70) is 1.8451, times 70.041 gives 129.2. Then 108.0 - 129.2 + 36.76 = 15.5 percent.
Work the women's example: waist 28, hip 38, neck 13, height 64. The combined term is 28 + 38 - 13 = 53, log10(53) is 1.7243, times 163.205 gives 281.4. Log10(64) is 1.8062, times 97.684 gives 176.4. Then 281.4 - 176.4 - 78.39 = 26.6 percent.
Categories differ by sex because essential fat differs. For men: essential 2-5, athletes 6-13, fitness 14-17, average 18-24, obesity 25+. For women: essential 10-13, athletes 14-20, fitness 21-24, average 25-31, obesity 32+. Our examples land in men's fitness and women's average.
Measure correctly or the formula punishes you. Waist goes around the navel, relaxed, after exhaling. Neck goes just below the Adam's apple. Hips go around the widest point. The tape should be snug against skin without denting it, and every measurement should be repeated twice.
Body fat calculator questions
How accurate is the Navy body fat method?
The Navy method typically lands within 3 to 4 percentage points of DEXA scans for average builds. It is excellent for tracking change over time with consistent measuring technique, but it is not a medical-grade measurement. Very muscular or very lean people see larger errors.
What measurements do I need?
Men need height, neck circumference, and waist circumference. Women add hip circumference. The calculator accepts inches or centimeters and converts internally. Measure waist at the navel relaxed, neck below the Adam's apple, and hips at the widest point.
What is a healthy body fat percentage?
For men, 14 to 17 percent is the fitness range and 18 to 24 is average; for women, 21 to 24 is fitness and 25 to 31 is average. Below essential levels (under 6 for men, under 14 for women) brings health risks, so lower is not always better.
Why do men and women use different formulas?
Women carry more essential fat and distribute it differently, with hips capturing lower-body fat the men's formula would miss. The separate equations and category bands reflect those physiological differences.