Estimated body fat
This calculator estimates your body fat percentage from a few simple tape-measure readings using the U.S. Navy circumference method. It is a quick, no-equipment way to get a number you can track over time, without a caliper, scale, or body scan. A scale tells you total weight; this tells you roughly how much of that weight is fat versus muscle, bone, and water — which is what actually changes when you train or diet.
The method is built on a simple observation: fat tends to collect around the midsection, so the gap between your waist and neck tracks body fat reasonably well once height is accounted for. The formula takes the log of those measurements rather than the raw inches, which is why a one-inch change at the waist matters more on a lean frame than a heavy one. For men it uses height, neck, and waist. For women it adds the hip measurement, because women carry more fat below the waist and the men's equation would underestimate it.
Here is the male equation worked through, so the number isn't a black box. Take a man 70 inches tall with a 15-inch neck and a 34-inch waist:
Notice the waist is the only number you can really move month to month. If that same man's waist grows from 34 to 38 inches with everything else unchanged, the estimate climbs from 11.1% to 18% (Average); at 40 inches it reaches 21%. That is the leverage the tape measure gives you — a four-inch swing at the waist is the difference between an athletic and an average reading.
The formula is only as good as the tape work, and a half-inch error on the waist can shift the result by a percentage point or more. Use a flexible cloth tape, not a metal one, and measure on bare skin.
The honest answer: it is an estimate, not a measurement. Lab methods like a DEXA scan or hydrostatic weighing actually quantify fat tissue; the Navy method only infers it from three or four circumferences, so it can't see where your fat sits or how much muscle you carry. Published validations generally put it within roughly 3 to 4 percentage points of a DEXA reading for average-build adults — close enough to be useful, not close enough to obsess over the decimal.
It drifts most for two groups. Very lean, muscular people (think a lifter with a thick neck and tight waist) often read a touch high, and people carrying weight unusually — a slim waist with heavier legs, for instance — can read low because the tape never sees that fat. That is the method's core limitation: it assumes your fat is distributed in the typical pattern its formula was fitted to.
The calculator labels your result using common reference ranges. For men those are roughly: essential fat under 6%, athletes 6 to 13%, fitness 14 to 17%, average 18 to 24%, and above average at 25% and up. Women's ranges run higher across the board because more fat is essential — childbearing and hormones require it. Lower is not automatically healthier: dropping below the essential floor carries real risks, and chasing single-digit numbers is a goal for stage competitors, not general health.
Treat one reading as a baseline, not a verdict. The number moves with hydration, a big meal, and time of day, so a single measurement can be off by a point in either direction. What's reliable is the trend: measure under the same conditions each time — first thing in the morning, before eating or drinking, after using the bathroom — and watch the direction over weeks, not days.
How does the U.S. Navy method work?
It estimates body fat from a few tape-measure readings — height, neck, and waist for men, plus hips for women — instead of a skinfold caliper or scan. The measurements feed a formula based on the relationship between waist size and body fat.
How accurate is it?
For most people it lands within a few percentage points of a clinical reading, which is good enough to track changes over time. It is less reliable for very lean athletes or anyone with an unusual build, so treat it as a guide, not a diagnosis.
Where exactly do I measure?
Measure the neck just below the larynx, the waist at the navel for men and at the narrowest point for women, and the hips at the widest point. Keep the tape level and snug without compressing the skin.
What is a healthy body fat percentage?
Common fitness ranges are about 14 to 17 percent for men and 21 to 24 percent for women, with athletes lower. Essential fat sits near 2 to 5 percent for men and 10 to 13 percent for women. Healthy ranges vary by age and goals.
Last reviewed June 2026. Uses the U.S. Navy circumference method. For general guidance, not medical advice.