Scale weight alone hides one of the most encouraging outcomes in training: body recomposition, where someone loses fat and gains muscle at the same time, leaving total weight almost unchanged while their body fat percentage drops meaningfully. Someone tracking only the scale during this process would see no progress and could get discouraged despite a genuinely successful few months of training — which is exactly why body fat percentage is the more informative number for anyone lifting weights while managing their weight.

For weight-class sports specifically — boxing, wrestling, judo, powerlifting — body fat percentage matters differently than it does for general health, since athletes there are managing the trade-off between making a weight category and retaining the muscle mass that produces strength and power at that weight. General population healthy ranges don't map cleanly onto what a competitive athlete making weight should target.

No circumference-based method, including the US Navy formula used here, replaces clinical-grade tools like DEXA scanning for precise, one-time measurement — but for tracking your own trend over months with a consistent method and consistent measurement technique, the relative change tells you much more than any single reading's absolute accuracy.