Calculate your Lean Body Mass (LBM) using Boer, James, Hume formulas or direct body fat percentage. Track muscle mass changes and composition stats.
Calculations run locally in client-side Javascript. No weight, height, or fat measurements are uploaded to servers.
Select a profile to load its composition values instantly:
Fill in your physical weight, height, gender, and fat parameters to calculate your lean body mass breakdown.
FFMI evaluates total muscle tissue density normalized to stature. Higher values correspond to robust skeletal frame and higher athletic potential.
Typical healthy lean mass and body fat percentage thresholds classified by biological gender.
Women require higher essential body fat levels (10-13%) compared to men to support reproductive health, hormonal balance, and endocrine functions. Consequently, the healthy lean mass baseline percentage range is slightly lower.
| LBM Percentage | Body Fat Equivalent | Category Description |
|---|---|---|
| 87.0% - 90.0% | 10.0% - 13.0% | Essential Fat Only (Stage lean) |
| 80.0% - 86.0% | 14.0% - 20.0% | Athletes / High Muscle Outline |
| 76.0% - 79.0% | 21.0% - 24.0% | Fitness / Fit Athletic Range |
| 69.0% - 75.0% | 25.0% - 31.0% | Average / Normal Store |
| < 68.0% | ≥ 32.0% | Over-fat / Obese Class Range |
Men naturally have a larger skeletal mass and lower physiological fat demands (2-5% essential fat). The healthy lean mass percentage baseline is consequently higher. Ratios below 75% lean mass indicate potential fitness adjustments.
| LBM Percentage | Body Fat Equivalent | Category Description |
|---|---|---|
| 95.0% - 98.0% | 2.0% - 5.0% | Essential Fat Only (Stage lean) |
| 87.0% - 94.0% | 6.0% - 13.0% | Athletes / High Muscle Outline |
| 83.0% - 86.0% | 14.0% - 17.0% | Fitness / Fit Athletic Range |
| 76.0% - 82.0% | 18.0% - 24.0% | Average / Normal Store |
| < 75.0% | ≥ 25.0% | Over-fat / Obese Class Range |
Understanding fat-free mass index, muscle hypertrophy dynamics, and accurate body composition tracking.
**Lean Body Mass (LBM)** is the weight of everything in the body except for adipose (fat) tissue. It is divided into:
To stimulate muscle growth (hypertrophy) and protect LBM during caloric restriction, you must create a stimulus via progressive overload strength training, and feed amino acids via dietary protein. Consuming **1.6 to 2.2 grams of protein per kilogram** of body weight triggers muscle protein synthesis (MPS) and helps block muscle tissue oxidation.
While BMI measures weight vs height without noting fat, **FFMI** isolates your relative muscle mass. Natural bodybuilders typically hit an upper ceiling around an FFMI of 25. Anything between 22 and 24 indicates superior natural muscle density, whereas values below 18 for men suggest potential benefits from additional resistance training.
Shedding pounds blindly on a scale can result in losing skeletal muscle instead of fat. Severe caloric deficits combined with poor protein intake force the body to strip amino acids from muscle fibers for fuel. Focus on a **moderate caloric deficit** (300-500 calories) to ensure your weight loss is fat loss while your Lean Body Mass stays protected.
Relying only on the scale can hide progress since you might gain muscle and lose fat simultaneously (body recomposition), leaving scale weight unchanged. Optimize your tracking by:
When body fat is unknown, the calculator uses clinical equations. The **Boer** and **Hume** formulas are linear systems widely validated in drug dosage calibrations, whereas the **James** formula uses non-linear height-to-weight ratios. The calculator averages all three to counter any individual bias at extreme heights or weights.
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Lean Body Mass is the total weight of your body minus your fat mass. It includes skeletal muscle, bones, organs, blood, connective tissue, and water content. LBM is the metabolically active tissue that burns calories even at rest.
If you know your body fat percentage, LBM is calculated directly as: Weight * (1 - Body Fat% / 100). If you do not know it, the calculator uses the Boer (1984), James (1976), and Hume (1966) equations, which estimate LBM based on your height, weight, and biological gender.
FFMI is a metric that evaluates your muscle mass relative to your height, similar to how BMI evaluates total weight. It is calculated as LBM (kg) / Height (m)². A normalized FFMI adjusts for heights different from 1.8 meters, allowing comparison of muscularity across individuals.
Ideal LBM depends on gender, age, and fitness goals. Typically, a healthy LBM range is 76% to 92% of total weight for men (corresponding to 8% to 24% body fat) and 69% to 80% of total weight for women (corresponding to 20% to 31% body fat).
You can increase your LBM by engaging in regular progressive resistance training (weightlifting), consuming adequate dietary protein (typically 1.6 to 2.2g per kg of body weight), ensuring proper recovery/sleep, and maintaining a slight caloric surplus or a minor deficit (during body recomposition).
Read our in-depth articles and guides related to this tool to help you make smarter decisions.
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