Body Fat Calculator

How It Works

The U.S. Navy body fat method estimates body composition from circumference measurements alone — no scales-while-underwater, no scans. It dates to 1985 circumference studies run for the U.S. Navy, where tape measurements were statistically fitted against hydrostatic (underwater) weighing; the resulting equations are logarithmic fits, which is why the formula below uses log10 of inches.

The formula (measurements in inches)

Men: % fat = 86.010 × log10(waist − neck) − 70.041 × log10(height) + 36.76
Women: % fat = 163.205 × log10(waist + hips − neck) − 97.684 × log10(height) − 78.387

Why women add a hip measurement

Adult women typically store a larger share of body fat on the hips, buttocks and thighs, so waist alone under-describes total fat for them. Adding the widest hip circumference into the waist + hips − neck term re-balances the fit against the reference method; men's fat pattern is centered enough that the Navy data did not need a hip term.

Known biases

Like any regression from population data, the method has systematic limits: comparisons with DEXA suggest it tends to slightly overestimate body fat in leaner adults and slightly underestimate it at higher BMIs, and results move noticeably with small tape placement errors. Treat a single reading as approximate and watch trends over repeated measurements under the same conditions.

Frequently Asked Questions