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Body-fat percentage via the US Navy tape method, split into fat mass and lean mass.
US Navy: men 86.010·log₁₀(waist−neck) − 70.041·log₁₀(height) + 36.76
Hip is used for the female formula.
It estimates body-fat percentage from a few tape measurements — neck and waist for men, plus hips for women — together with height. It was developed so body composition could be checked without special equipment, using only a tape measure. It is an approximation, not the lab-grade accuracy of a DEXA scan or hydrostatic weighing.
The formula includes a height term, so an accurate height changes the result — that is why height is one of the inputs here even though some summaries leave it out. The equation was published using inches, so this calculator takes its measurements in inches to match the original coefficients exactly.
Fat mass is the weight of body fat. Lean mass is everything else — muscle, bone, organs, and water. Your total body weight is the two added together, so once the percentage is known, multiplying by your weight splits it into those two parts.
The ring is your whole body weight. One arc is fat mass and the other is lean mass, sized by their share of the total. Seeing them side by side makes the percentage concrete: a thin fat arc and a large lean arc means most of your weight is muscle, bone and water.
It is a practical field estimate — used by the military, gyms, and anyone tracking change over time with just a tape measure. Because it is approximate, the most useful thing is the trend: measuring the same way each month shows direction even if the absolute number is a little off. For a precise figure, a clinical body-composition scan is the gold standard.