Calculate your lean body mass (muscle, bone, organs) using the Boer formula.
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Lean body mass (LBM) represents everything in your body that isn't fat — muscle, bone, organs, and water. Tracking LBM alongside body fat percentage gives a fuller picture of body composition than weight alone, which is especially useful for athletes and anyone in a fitness or nutrition program. The Boer formula used here is one of the most validated equations for estimating LBM from simple height and weight measurements. Lean body mass includes everything that isn't fat — muscle, bone, organs, connective tissue, and contained water — typically 60-90% of total body weight depending on fat percentage, sex, and age. It matters clinically because some medication dosing depends on lean mass rather than total weight, and in fitness it defines the real goal of most training: gaining or preserving this mass while losing fat, not just losing weight regardless of source. Because this figure is derived from an estimation formula rather than a direct scan, it works best as a tracking tool alongside body weight and, ideally, an occasional body fat percentage measurement — together, these three numbers tell a much more complete story about actual body composition changes than any single measurement alone ever could.
Lean body mass refers to everything in the body that isn't fat tissue — muscle, bone, organs, connective tissue, and the water contained within all of it — and it typically makes up somewhere between 60-90% of total body weight depending on body fat percentage, sex, and muscularity. Unlike fat-free mass (a very similar but technically distinct term used in some formulas), lean body mass calculations sometimes include a small essential fat component, since some fat is structurally necessary and can't realistically be separated from lean tissue in a simple weight-based calculation.
This calculator uses the Boer formula, developed in 1984 as an update to older methods, using height, weight, and biological sex as inputs — sex is included because men and women have systematically different average ratios of muscle, bone density, and essential fat even at identical height and weight, largely due to hormonal differences. The Boer formula is one of several competing equations (alongside James and Hume formulas, among others), and like most anthropometric estimation methods, all of them are approximations rather than a direct measurement — an actual DEXA scan or bioelectrical impedance analysis provides considerably more individualized precision.
Lean body mass matters clinically and practically for several reasons beyond simple curiosity: it's a more physiologically accurate basis for calculating protein needs than total body weight, since protein is used to build and repair lean tissue specifically, not fat. It's also used in some medical contexts for more precise medication dosing, since many drugs distribute through lean tissue rather than fat, and it provides a more meaningful baseline than total weight for tracking whether a weight-loss or muscle-building program is actually changing body composition in the intended direction, rather than just moving the number on a scale.
Tracking lean body mass over time — ideally alongside a consistent body fat percentage measurement — gives a clearer picture of whether weight changes reflect fat loss, muscle gain, water fluctuation, or some combination, which the number on a scale alone can never reveal.
Weight alone doesn't tell you if you're gaining muscle or fat — LBM helps separate the two.
Yes — that's actually the ideal outcome of most weight-loss plans: losing fat mass while preserving (or even growing) lean mass through adequate protein intake and resistance training during the process.
Yes, primarily through resistance training and adequate protein intake.