Body Fat Calculator
The US Navy circumference method. Tape measure in centimetres, no calipers needed.
Worked example
Neck 38, waist 85 and height 175 gives roughly 15% by the Navy formula. The same waist on a shorter frame reads higher, because height is part of the denominator.
The Navy method assumes body fat distributes predictably relative to circumference. It is accurate to about ±3–4 percentage points for most people, and considerably worse for very muscular or very lean individuals, where neck and waist do not move the way the formula expects.
Measuring consistently
Measure at the same time of day, relaxed, tape flat against the skin without compressing. A one-centimetre error at the waist moves the result by about half a percentage point, so consistency between measurements matters more than absolute precision.