Lean Body Mass Calculator
Estimate lean body mass from body weight and body-fat percentage, with a clear breakdown of lean mass and estimated fat mass.
Calculate lean body mass
Enter your weight and a body-fat estimate.
The result depends on the accuracy of your body-fat estimate.
Your body-composition breakdown
Lean mass and fat mass are parts of total body weight.
This graphic visualizes your entered body-fat percentage. It does not measure muscle directly or indicate whether a body composition is healthy for you.
What is lean body mass?
Lean body mass (LBM) describes body weight excluding body fat, using the definition and measurement method chosen. It includes muscle, bone, organs, connective tissue and body water. It is not the same as skeletal muscle mass, so a lean body mass estimate should not be interpreted as the amount of muscle alone.
Some calculators estimate LBM from height, weight, age and sex using published equations. This page uses the simpler approach when a body-fat percentage is available: subtract estimated fat mass from total body weight. The result is only as reliable as the body-fat input.
Lean body mass formula
Lean body mass = body weight × (1 − body-fat percentage ÷ 100)
Fat mass = body weight × body-fat percentage ÷ 100
Worked example
If body weight is 70 kg and estimated body fat is 20%, fat mass is 70 × 0.20 = 14 kg. Lean body mass is 70 − 14 = 56 kg. The same calculation works in pounds as long as weight and the resulting masses use the same unit.
How to interpret your result
📏 Body-fat accuracy matters
Body-fat estimates from scales, skinfolds, tape-based equations and scans can differ. If the input is off by several percentage points, the calculated lean mass will also change.
💪 Lean mass is not muscle mass
Lean body mass includes several non-fat tissues, not just muscle. Do not use this result as a direct measurement of muscle growth or strength.
📈 Track trends consistently
If you monitor changes, use similar measurement conditions and the same method where possible. Hydration, meals, exercise and measurement technique can affect body-composition estimates.
🧭 Consider the bigger picture
Body composition is one metric among many. Strength, endurance, energy, sleep, health markers and how you feel can also matter when evaluating fitness progress.
Frequently asked questions
How do I calculate lean body mass?
Multiply body weight by one minus the body-fat fraction. For example, at 20% body fat, use 1 − 0.20 = 0.80. Multiply your weight by 0.80 to estimate lean body mass.
Is lean body mass the same as fat-free mass?
The terms are often used similarly in everyday fitness settings, but some technical definitions distinguish them because lean body mass may include essential lipids. The measurement method and context matter.
Can I calculate LBM without knowing body fat?
This calculator requires a body-fat percentage. Other equations estimate LBM from height, weight and sex, but they are population-based estimates and can differ from a result based on measured body fat.
Does higher lean body mass always mean better health?
Not on its own. Interpretation depends on body size, age, sex, health status and the method used. A single number cannot establish health or fitness.
How often should I recalculate?
Recalculate when you have a meaningful new measurement rather than reacting to daily fluctuations. If tracking progress, use a consistent measurement method and consider trends over time.
Important: This tool is for general education and does not diagnose a health condition. Body-composition estimates can be inaccurate and should not be used alone to make medical or nutrition decisions.