Lean Body Mass Calculator
Calculate your fat-free body mass using proven formulas
LBM Formulas
Understanding Lean Body Mass
Lean Body Mass (LBM), also called Fat-Free Mass (FFM), is your total body weight minus all fat tissue. It includes muscles, bones, organs, skin, blood, and water. LBM is a more meaningful metric than total weight for assessing fitness and health.
Unlike body fat percentage which focuses on what you want to lose, LBM focuses on what you want to preserve or build. When dieting, the goal is to lose fat while maintaining LBM. When building muscle, the goal is to increase LBM without excessive fat gain.
Knowing your LBM helps set realistic protein intake (0.7-1g per pound LBM), calculate medication dosages, assess metabolic health, and track body composition changes over time.
LBM Calculation Methods
Boer Formula
Most accurate for normal BMI. Uses weight and height. Separate formulas for men/women.
James Formula
Good for general population. May overestimate LBM in obese individuals.
Hume Formula
Often used in clinical settings. Similar accuracy to Boer for most people.
Body Fat Method
Most accurate when BF% is measured directly (DEXA, hydrostatic, etc.).
Typical Lean Body Mass Ranges
| Category | Men (% of weight) | Women (% of weight) | Notes |
|---|---|---|---|
| Essential Fat | 75-80% | 68-75% | Minimum healthy LBM |
| Athletes | 85-95% | 78-88% | High muscle, low fat |
| Fitness | 80-90% | 75-85% | Above average |
| Average | 75-85% | 70-80% | Typical healthy adult |
| Overweight | 65-75% | 60-70% | Higher fat percentage |
Using LBM for Fitness Goals
Protein Needs
Base protein intake on LBM, not total weight. Aim for 0.7-1g protein per pound of LBM for muscle maintenance/growth.
Track Progress
Weight fluctuates with water, but LBM changes slowly. Track LBM monthly to see true muscle gains or losses.
Body Recomposition
If weight stays stable but LBM increases, you're building muscle and losing fat simultaneously—ideal outcome.
Strength Goals
More LBM generally means more strength potential. Focus on progressive overload to build LBM.
Frequently Asked Questions
What is a good lean body mass for my height?
There's no single answer—it depends on your goals, genetics, and activity level. As a rough guide, a fit man might have LBM around 75-80% of 'ideal' body weight, women 68-75%. Focus on trends rather than absolute numbers.
Can I increase my lean body mass?
Yes, through resistance training and adequate protein intake. Beginners can gain 1-2 lbs of muscle per month; experienced lifters may gain 0.25-0.5 lbs monthly. Progressive overload and recovery are key.
Why are there different LBM formulas?
Each formula was developed from different study populations. No formula is perfect for everyone. Using multiple formulas and averaging gives a better estimate. For precise measurement, use DEXA or hydrostatic weighing.
Does LBM include water weight?
Yes, LBM includes all non-fat mass: muscle, bone, organs, and water. This is why LBM can fluctuate 2-5 lbs daily based on hydration. For accurate trends, measure at consistent times.
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