Body Fat Calculator

This calculator uses the US Navy circumference method, which estimates body fat from a tape measure rather than a scale. For men it uses height, neck and waist. For women it adds hip circumference because fat distribution differs around the pelvis. The numbers go through a logarithmic formula and you get a percentage out the other end.

Measure first thing in the morning before food or water, standing relaxed. Neck just below the larynx, waist at the navel for men or the narrowest point for women, hips at the widest part of the buttocks. A small mistake (1cm out on the waist) shifts the result by about 1% body fat, so do each measurement twice and use the average.

If you have ever had body fat measured three different ways and got three answers, you are not alone. Skinfold calipers tend to read 2-3% lower than the Navy tape method. Bioelectrical impedance (BIA) scales swing wildly with hydration, often varying by 4-5% from morning to evening. DEXA scans are the closest thing to a gold standard but typically read 3-5% higher than tape methods.

The trick is to pick one method and stick with it for tracking. A woman starting at 28% by Navy method who reaches 24% three months later by Navy method has lost real fat. Comparing her starting Navy reading to a final DEXA reading tells her almost nothing. The trend matters far more than the absolute number.