Body Fat Calculator

Body fat percentage answers a question the bathroom scale can't: how much of your weight is fat versus everything else? Two people at the same weight and height can look and feel completely different because of it — which is why athletes and trainers track body fat, not just weight, and why BMI (which can't tell muscle from fat) misclassifies muscular people.

This calculator implements the US Navy circumference method, developed for exactly this situation: a decent estimate from nothing but a tape measure. Men measure neck and waist; women add hips; the logarithmic formula (printed on the tool) converts the measurements and height into a percentage. Validation studies put it within roughly 3–4% of laboratory methods for most people — meaningfully less precise than a DEXA scan, meaningfully more informative than weight alone, and free.

The result comes with the American Council on Exercise category bands (essential fat, athletes, fitness, average, obese — different for men and women, because women's essential fat is physiologically higher), plus measurement instructions, because technique drives accuracy: tape snug but not compressing, waist at the navel for men and the narrowest point for women. The most valuable use isn't the one-off number — it's the trend when you re-measure the same way every few weeks.