Lean body mass is the part of you worth protecting on any diet. It represents your muscle, bone and organs — the tissue that keeps your metabolism high and your body strong.
Two ways to calculate it
The most accurate method subtracts fat mass (from a body-fat measurement) from total weight. When body fat is unknown, predictive equations like Boer estimate LBM from height, weight and sex.
Using LBM
Lean mass is a useful anchor for setting protein intake and for judging whether a fat-loss phase is costing you muscle. Watch it alongside body-fat percentage over time.
Frequently asked questions
Lean body mass is your total weight minus fat mass — it includes muscle, bone, organs and water. It's a key driver of your resting metabolism and strength.
If you know your body-fat percentage: LBM = weight × (1 − bodyfat%/100). Without it, formulas like Boer estimate LBM from your height, weight and sex.
More lean mass means a higher metabolic rate, better strength and a healthier body composition. Protecting it during fat loss is why protein and resistance training are essential.