Body Fat Calculator (US Navy Method)

A US Navy body fat calculator that turns a few tape-measure readings into your estimated body fat percentage, the fitness category it falls into, and — if you add your weight — your fat mass and lean mass. It is built for anyone who wants a free, private body-composition check without skinfold calipers, smart scales or a clinic visit. You only need a soft measuring tape and a wall to stand against.

How it works

The US Navy circumference method was developed so service members could be assessed with nothing more than a tape measure, yet still track reasonably close to underwater weighing. Instead of pinching skinfolds, it relies on the fact that fat tends to accumulate at predictable places — the waist and, for women, the hips — relative to leaner reference points like the neck and overall height.

For men the model uses height, neck and waist; for women it adds the hip, because female fat distribution needs that extra measurement to stay accurate. Each value is fed into a logarithmic regression equation. This tool converts every input to centimetres first (so imperial and metric give identical answers), evaluates the formula, then clamps the output to a sensible physiological range. It also maps your result onto the American Council on Exercise category bands — essential, athletes, fitness, average and obese — using separate thresholds for men and women, and shows a colour scale with a marker at your value.

Because the method only sees circumferences, it cannot tell dense muscle from fat. That is why a very muscular athlete with a thick waist may read slightly high, and a very lean person may read slightly low. Treat the number as a consistent way to track change over weeks, not as a clinical verdict. For the most reliable trend, measure at the same time of day, on bare skin, after a normal exhale, and re-measure each site twice.

Worked example

Take a man who is 178 cm tall with a 38 cm neck and a 90 cm waist. The waist minus neck is 52 cm. Plugging into the male formula gives roughly 20.4% body fat, which lands in the “average / acceptable” band. If he also enters an 80 kg body weight, the tool reports about 16.3 kg of fat mass and 63.7 kg of lean mass, plus a BMI of 25.2 as a cross-check.

For a woman who is 165 cm tall with a 32 cm neck, 74 cm waist and 98 cm hip, the waist plus hip minus neck is 140 cm, and the female formula returns roughly 27% body fat — in the “average / acceptable” range for women.

Formula note: lengths must be in the same unit before the logs are taken, and the waist must exceed the neck (men) or waist + hip must exceed the neck (women); otherwise the log argument turns non-positive and the estimate is undefined. This calculator guards for that and asks you to re-check the measurements rather than printing a nonsense number.

Every figure is computed in your browser — no measurements are uploaded or stored.