Body fat
calculator
No calipers, no scan — a tape measure and the US Navy's circumference formula give a respectable body-fat estimate. Measure, enter, and see where you land.
How the Navy method works
Developed for fleet-wide fitness screening, the US Navy method estimates body fat from the circumferences that track it best — waist and neck for men, plus hips for women — combined with height in a logarithmic formula. It needs nothing but a tape measure and honest technique.
Measuring right
Waist at the navel, relaxed, tape snug but not compressing. Neck just below the larynx, tape sloping slightly down at the front. Hips at the widest point. Same time of day each check — morning, before food, is most repeatable.
Accuracy, honestly
Against lab methods like DEXA, circumference formulas typically land within ±3–4 percentage points — decent for tracking direction over months, not a lab result. Very muscular or very lean bodies read least accurately. Use the trend, not one reading. For related metrics, see BMI and ideal weight.
Body fat % FAQ
It estimates body fat from tape measurements — waist and neck for men, plus hips for women — combined with height in a validated logarithmic formula developed for US Navy fitness screening.
Typically within ±3–4 percentage points of lab methods like DEXA. Fine for tracking your trend over months; least accurate at very muscular or very lean extremes.
Common fitness references (ACE): for men, 6–24% spans athlete to average, with 25%+ above average; for women, 14–31%, with 32%+ above average. Essential fat is roughly 2–5% (men) and 10–13% (women).
Tape position, tension, hydration and food timing all move readings. Standardize: same spots, same tension, morning before eating — and judge by the multi-week trend.