Body fat estimator

This estimator is the US Navy circumference method, implemented with the constants in the form on this site. It is a tape-measure estimate. It is not a DEXA scan, and a single reading can sit several points away from a lab method. The useful output is the direction of repeated readings taken the same way.

The inputs and the two equations

Everyone enters height, neck, and waist in inches. The female selection also requires hip. Weight in pounds is optional and is used only to split the result into lean mass and fat mass. It does not change the body-fat percentage. For the male selection the page computes 86.010 times the base-10 log of waist minus neck, minus 70.041 times the base-10 log of height, plus 36.76. For the female selection it computes 163.205 times the base-10 log of waist plus hip minus neck, minus 97.684 times the base-10 log of height, minus 78.387. The result is clamped between 3 and 60 percent and rounded to one decimal. If waist is not larger than neck, the male log is undefined and the form should be treated as a bad measurement, not as a body-fat of zero.

The category label is a bucket, not a diagnosis

The label on the result uses the same cut points for both sex selections: under 6 essential, under 14 athletic, under 18 fitness, under 25 average, and the rest above average. Those cuts are a display choice on this page. Published category charts usually differ for men and women, and essential fat is not a target to chase. Do not diet toward the essential bucket because the word showed up in the box. Measure in the morning, before a large meal, with the tape in the same place each time. Neck is below the larynx, waist is at the navel for this style of estimate, and hip is the widest point. A tighter tape position next week is not fat loss.

Use the percentage to decide whether the calorie target from the macro calculator is doing what you wanted over a month, not to judge a single Tuesday. The form is also on the tools hub.