How the lean mass calculator works
What "lean mass" actually contains
Lean body mass is everything that is not fat: muscle, bone, organs, blood, and water — roughly 70–75% water by weight. This is why strength athletes track it (it proxies the muscle that lifts), why cuts that preserve it preserve performance, and why dehydrated weigh-ins "lose lean mass" that reappears with a salt shaker.
The target-weight calculation
Keep lean mass constant and solve for weight at goal body fat: target = lean ÷ (1 − goal%). A 190-lb person at 22% has 148 lb of lean; at 15% that lean weighs 174 lb. The 16-lb gap is the fat-only version of the goal — reality lands a few pounds higher because cuts shed some lean mass, which is a plan, not a failure.
Why composition beats scale weight
Two people at 180 lb can be a strong, healthy athlete and a sedentary high-risk build. The scale reports total; composition reports what matters: the fat line falling and the lean line holding. Progress photos plus this calculator make that visible long before the scale agrees.