Enter your body weight and body fat percentage to see your lean body mass (everything except fat: muscle, bone, organs, water). Useful for fitness tracking, macro calculations, and understanding body composition.
Lean body mass (LBM) is your total body weight minus your fat mass. It includes muscle, bone, organs, blood, water, and connective tissue — essentially everything in your body except adipose (fat) tissue. For a 180-pound adult with 20% body fat, fat mass is 36 pounds and lean body mass is 144 pounds. The two together make up total body weight.
LBM matters for several practical reasons. It's the metabolically active component of your body — most resting calorie burn (BMR) comes from lean tissue, especially muscle. Two people of the same weight can have very different BMRs if their LBM differs substantially. LBM is also the right basis for calculating protein needs (typically 0.6-1.0g per pound of LBM for athletic populations), some medication dosages, and body composition tracking during weight management.
This calculator computes LBM from total weight and body fat percentage. It also shows fat mass and the LBM-to-weight ratio (an indicator of body composition). Use it for: protein target calculation (more accurate than per-pound-of-bodyweight for very lean or very obese individuals), tracking body composition changes over time (the scale weight alone doesn't show whether you're losing fat vs. muscle), and understanding how body composition relates to overall fitness. For accurate body fat measurement, use the body-fat calculator (Navy tape method) or get a DEXA scan; this calculator depends on knowing your body fat percentage as an input.
190 lbs, 24% body fat. Fat mass: 45.6 lbs LBM: 144.4 lbs LBM % of body weight: 76% Typical for a middle-aged moderately active adult. Higher protein at 0.8g/lb LBM = 115g/day. Resistance training would aim to gradually increase LBM while reducing body fat.
135 lbs, 18% body fat. Fat mass: 24.3 lbs LBM: 110.7 lbs LBM % of body weight: 82% Athletic body composition. Higher protein at 0.9g/lb LBM = 100g/day to maintain muscle during training. Lower body fat than typical population indicates effective training and nutrition.
Starting: 220 lbs, 32% body fat. LBM 150 lbs, fat 70 lbs. After 6 months of weight loss + resistance training: 195 lbs, 24% body fat. LBM 148 lbs, fat 47 lbs. Total weight loss: 25 lbs. But composition change: fat loss 23 lbs, LBM loss only 2 lbs. The vast majority of weight lost was fat — the goal of successful body recomposition. Without LBM tracking (just total weight), this looks like "25 lb weight loss." With LBM tracking, the success of preserving muscle while losing fat is visible — the body composition outcome is excellent. Failed alternative: aggressive crash dieting without resistance training often produces "25 lb weight loss" composed of 15 lbs fat + 10 lbs muscle. Same scale number, much worse body composition outcome.
Use this calculator when tracking body composition changes, calculating protein needs (especially for individuals at body fat extremes), planning weight management programs, or understanding how lean tissue contributes to overall body weight.
Pair with: body-fat calculator (provides the body fat % input), BMR and TDEE calculators (since LBM drives metabolic rate), protein and macro calculators (LBM-based protein targets are often more accurate than bodyweight-based), and ideal-weight calculator (for healthy weight range comparison).
For most casual fitness purposes, total body weight tracking is sufficient. LBM tracking becomes more useful for: serious resistance trainers (muscle gain goals), individuals losing significant weight (preserving LBM is critical), elderly fighting sarcopenia (LBM loss is a major health concern), and anyone with body fat percentage substantially above or below typical (where bodyweight badly approximates lean tissue).
For most accurate body composition measurement: DEXA scans (gold standard, ~$50-150 per scan, available at fitness research centers). Hydrostatic underwater weighing (very accurate but rare equipment). Bod Pod (air displacement, less common). Bioimpedance scales and handheld devices (convenient but less accurate; readings vary 3-8% based on hydration). The Navy tape method (in the body-fat calculator) is reasonably accurate for most healthy adults.
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Lean Body Mass
144.0 lbs
Fat Mass
36.0 lbs
Lean %
80.0%
| Metric | Value |
|---|---|
| Total Weight | 180.0 lbs / 81.6 kg |
| Body Fat % | 20.0% |
| Lean Body Mass | 144.0 lbs / 65.3 kg |
| Lean Mass % | 80.0% |
| Fat Mass | 36.0 lbs / 16.3 kg |