Body Fat % (US Navy Method)

Overview

The US Navy body fat method estimates body fat percentage from a handful of tape-measure circumferences and your height. It was developed for military recruiters who needed a quick, equipment-light alternative to skinfold callipers or hydrostatic weighing, and it remains popular in gyms and fitness apps because it requires nothing more than a soft tape and a mirror.

Compared to a single body-mass-index reading, this method distinguishes between muscle and fat, which is important for active people whose BMI may flag them as overweight even at low body-fat percentages. Accuracy is typically within three to four points of more clinical methods, making it suitable for tracking progress over months rather than precise diagnostic use.

How it works

For men, the formula is %BF = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76. For women, hip circumference is added: %BF = 163.205 × log10(waist + hip − neck) − 97.684 × log10(height) − 78.387. All inputs are in inches and the logarithms are base-10. Internally the tool accepts centimetres too and converts before applying the equations.

The result is then mapped into qualitative bands — essential fat, athletic, fitness, average, obese — based on age and sex. Because the method assumes typical fat distribution, very lean or very heavy users may see larger errors, and a consistent measurement technique (same time of day, relaxed posture, tape flat against skin) matters more than absolute accuracy.

Examples

• A man with a 32 in waist, 15 in neck and 70 in height: 86.010 × log10(17) − 70.041 × log10(70) + 36.76 ≈ 14.7% body fat — athletic range.
• A man with a 40 in waist, 16 in neck and 70 in height climbs to roughly 26% body fat — above average.
• A woman with a 28 in waist, 38 in hip, 13 in neck, 65 in height: 163.205 × log10(53) − 97.684 × log10(65) − 78.387 ≈ 24.5% body fat — fitness range.
• The same woman five months later, waist 26 in and hip 37 in, drops to about 21% body fat.

FAQ

Where do I measure my waist?
For men, at the navel; for women, at the narrowest point above the hips, both with the tape level and snug but not compressing skin.

Why is hip only used for women?
Empirical fitting showed it improved accuracy for typical female fat distribution; it does not meaningfully help the male equation.

How accurate is it versus a DEXA scan?
Usually within three to four percentage points. Trend matters more than the absolute number.

Can I track weekly changes?
Daily measurements vary with hydration and digestion. Weekly or biweekly averages are more reliable.

Try Body Fat % (US Navy Method)