Body Fat Calculator
The US Navy tape method estimates body fat from a few circumference measurements. It needs nothing but a tape measure, and it tracks change far better than the bathroom scale does.
Measure your neck and waist, then enter them with your height.
Circumferences, not calipers.
This is the Hodgdon and Beckett equation the US Navy has used since 1984. For men it works from height and the difference between waist and neck. For women it adds the hips, because fat distribution differs enough that one equation cannot cover both.
How you measure matters more than the equation does. Keep the tape level and snug without compressing the skin, measure at the end of a normal breath out, and take every measurement the same way each time. Men measure the waist at the navel; women at the narrowest point. The neck goes just below the larynx, sloping slightly down at the front.
Expect roughly three to four percentage points of error against a DEXA scan. That is fine for the thing this is actually good at: measure monthly under the same conditions and the direction of travel is reliable even when the absolute number is not.
Numbers are the easy part.
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