The U.S. Navy method estimates body fat percentage from a few tape-measure circumferences rather than expensive scanning equipment. It's not as precise as a DEXA scan, but it's free, repeatable, and good enough to track trends over weeks and months.
Use this alongside the scale, not instead of it, especially if your weight isn't moving but your body seems to be changing shape — a common experience when building muscle while losing fat. Because it's a repeatable tape-measure method, it's most useful tracked every few weeks under consistent conditions, rather than as a single one-off number.
For men: 495 / (1.0324 - 0.19077 x log10(waist - neck) + 0.15456 x log10(height)) - 450. For women, the formula also factors in hip measurement: 495 / (1.29579 - 0.35004 x log10(waist + hip - neck) + 0.22100 x log10(height)) - 450. All measurements are in centimetres, taken at the narrowest point for the neck and waist.
Health Calc