Find your fat-free mass using the Boer formula — the equation independent validation studies rate as the most accurate for the general population.
Lean body mass is most useful when paired with your TDEE — it's what lets you set a calorie target that preserves muscle while losing fat.
Calculate My TDEE 🚀The number on a scale doesn't tell you what that weight actually is. Two people can both weigh 180 lbs, but one might carry 150 lbs of muscle and 30 lbs of fat, while the other carries 120 lbs of muscle and 60 lbs of fat. Lean body mass (LBM) separates the two, since it's everything in your body that isn't fat — muscle, bone, organs, water, and connective tissue.
| Formula | Notes |
|---|---|
| Boer (used here) | Validated against actual body composition measurements across a broad population. Generally considered the most accurate for general use. |
| James | An older formula, tends to be less accurate at higher body weights. |
| Hume | Similar accuracy to Boer, slightly different coefficients. |
All of these are estimates based on weight and height alone. For a more precise reading, methods like DEXA scans, hydrostatic weighing, or bioelectrical impedance scales account for your actual body composition rather than population averages — but those require equipment this calculator can't replicate.
This varies enormously by sex, age, and athletic background, so there's no single universal target. As a rough general reference, most healthy adult men carry 75-90% lean mass, and most healthy adult women carry 70-85% lean mass — women naturally carry more essential fat than men. Athletes and bodybuilders often sit above these ranges; this is normal and not something to chase as a universal goal.
Lean body mass includes muscle, but also bone, organs, water, and connective tissue. Muscle mass alone is just the muscle tissue portion of your LBM — so your LBM number will always be somewhat higher than your muscle mass alone.
Lean body mass (LBM) is the total weight of your body minus all fat mass. It includes your muscles, bones, organs, skin, water, and connective tissue — everything except stored body fat. It's a more clinically useful measure than total body weight because it reflects the metabolically active tissue in your body, which determines your resting metabolic rate and how your body responds to training and nutrition.
The most practical method without specialized equipment is a height and weight formula like the Boer formula used in this calculator. Enter your sex, weight, and height above and your lean body mass is calculated instantly. More precise methods include DEXA scanning (which separates bone, fat, and muscle tissue directly) or hydrostatic weighing — both require a clinic or specialized facility.
If you have body circumference measurements (neck, waist, hips), you can use the US Navy formula to first estimate body fat percentage, then subtract fat mass from total weight to get LBM. This calculator uses the Boer formula instead, which only requires height and weight — slightly less accurate for very muscular or very obese individuals, but practical for most people.
Yes, primarily through resistance training combined with adequate protein intake, ideally while in a calorie surplus or at maintenance. Significant LBM gains take months, not weeks — don't expect a meaningful change week to week.
Smart scales use bioelectrical impedance, which estimates body composition from how electrical current passes through your tissue — it's a different method than the population-based Boer formula used here, and both have their own margin of error. Treat both as estimates and track trends over time rather than comparing the two numbers directly.
No — see our Lean Body Mass vs. Muscle Mass guide for exactly what's included in each and why the difference matters for tracking progress.