Estimate your fat-free mass using three established formulas — Boer, Hume, and James. Understand how much of your weight is muscle, bone, and organs.
LBM estimates use population-based formulas and have a margin of error of 2-5 kg. For precise measurement, DEXA scanning or hydrostatic weighing is recommended. These estimates should not be used for clinical decisions.
Lean body mass (LBM) represents everything in your body that is not fat: skeletal muscle, bone, water, blood, organs, and connective tissue. It is sometimes used interchangeably with "fat-free mass," though technically LBM includes a small amount of essential fat found within organs and cell membranes (approximately 2–3% of body weight).
Knowing your lean body mass is valuable for several reasons. It determines your basal metabolic rate — more lean mass means you burn more calories at rest. It is a better indicator of physical fitness than total weight. And during weight loss, tracking LBM helps ensure you are losing fat, not muscle.
Generally considered the most accurate of the three. For men: LBM = 0.407 × weight + 0.267 × height − 19.2. For women: LBM = 0.252 × weight + 0.473 × height − 48.3. Weight in kg, height in cm.
One of the earliest LBM prediction equations. For men: LBM = 0.3281 × weight + 0.33929 × height − 29.5336. For women: LBM = 0.29569 × weight + 0.41813 × height − 43.2933.
Uses a slightly different mathematical approach. For men: LBM = 1.1 × weight − 128 × (weight/height)². For women: LBM = 1.07 × weight − 148 × (weight/height)².
| Category | Men (LBM as % of weight) | Women (LBM as % of weight) |
|---|---|---|
| Athletes | 80–90% | 75–85% |
| Fit individuals | 75–85% | 70–80% |
| Average | 70–80% | 65–75% |
| Above average body fat | Below 70% | Below 65% |
When people say they want to "lose weight," what they typically mean is they want to lose fat. But aggressive calorie restriction and insufficient protein intake can cause significant lean mass loss alongside fat loss. This is counterproductive because it reduces your metabolic rate (making further weight loss harder), weakens physical function, and can compromise bone density.
To preserve lean mass during a calorie deficit, research recommends adequate protein intake (1.6–2.2 g per kg of body weight), resistance training, and moderate rather than extreme calorie deficits. Use our macro calculator and calorie deficit calculator to set appropriate targets.
These formulas estimate LBM from height and weight only — they cannot measure actual body composition. Accuracy varies by 2–5 kg compared to DEXA scanning. The formulas may be less accurate for very muscular individuals, the elderly, or those at extremes of body fat. For precise lean mass measurement, consider DEXA scanning, bioelectrical impedance analysis (BIA), or hydrostatic weighing through a healthcare provider.
Everything in your body that is not fat: muscle, bone, water, organs, and connective tissue. It drives your basal metabolic rate and is a better indicator of fitness than total weight.
For men, 75–85% of total weight. For women, 68–78%. Athletes and muscular individuals may be higher.
It drives your metabolic rate, supports physical function and bone health, and helps you track whether you are losing fat or muscle during weight loss.
Typical margin of error is 2–5 kg compared to DEXA scanning. The Boer formula is generally the most accurate of the three.