Body fat calculator
Body fat calculator
Estimates body-fat percentage from tape measurements using the U.S. Navy circumference method. Measure relaxed, at the level described below.
Tape estimates carry a few points of error vs a DEXA scan. Track the trend over weeks, not a single reading.
How the estimate works
The U.S. Navy method uses the log of your circumference measurements and height to estimate body density, then converts that to a fat percentage. It is a tape-and-formula estimate, so it carries a few points of error versus a DEXA scan or hydrostatic weighing — but it is free, repeatable, and reliable for tracking change over time. Measure under the same conditions each time (morning, relaxed) so your trend is meaningful.
Why body fat beats the scale on a GLP-1
Weight alone can't distinguish fat from muscle. Because GLP-1 medications can drive fast weight loss — sometimes with inadequate protein — part of that loss can be lean mass. Re-measuring body fat every 2-4 weeks, together with tracking your strength, tells you whether you're losing fat (good) or muscle (fixable). If body-fat percentage isn't falling in step with the scale, raise protein toward the target in our macro calculator and add resistance training.
Body fat calculator FAQ
How does the U.S. Navy body fat method work?+
It estimates body fat from body circumferences — neck and waist for men, plus hip for women — combined with height. The formula was developed and validated by the U.S. Navy against hydrostatic weighing. It needs only a tape measure and is accurate to within a few percentage points for most people.
How do I measure correctly?+
Measure relaxed, without pulling the tape tight. Neck: just below the larynx, sloping slightly down at the front. Waist: at the navel for men, at the narrowest point for women. Hip (women): at the widest point. Take each measurement twice and average.
What is a healthy body fat percentage?+
For men, roughly 14-24% is the typical fitness-to-average range; for women, about 21-31%. Athletes sit lower. Essential fat (the minimum for health) is about 3-5% in men and 10-13% in women. Body fat trends matter more than a single reading.
Why track body fat on a GLP-1 instead of just weight?+
The scale can't tell fat loss from muscle loss. On a GLP-1, rapid weight loss with low protein can include muscle. Tracking body fat percentage over time — alongside strength — shows whether you are losing the right kind of weight. If body fat isn't dropping as fast as scale weight, raise protein and add resistance training.
Source
Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984 (Reports 84-11, 84-29).