Body Fat to Lean Mass Calculator
Calculate lean body mass, fat mass, muscle mass, and body composition analysis for tracking fitness progress.
Body Composition
Fat-Free Mass Index (FFMI)
FFMI Ranges (Men)
Body composition analysis breaks down your total body weight into different components:
- Lean Body Mass: Total weight minus fat mass (muscle, bone, organs, water)
- Fat Mass: Total body fat including essential and storage fat
- Muscle Mass: Skeletal muscle calculated using the Boer formula
- Bone Mass: Estimated bone weight (~15% for men, ~12% for women)
- Organ Mass: Internal organs, blood, and other lean tissue
These calculations provide insights into your body composition beyond just weight and BMI.
- FFMI measures lean body mass relative to height, similar to BMI
- More useful than BMI for athletes and muscular individuals
- Calculated as: Lean Body Mass (kg) ÷ Height (m)²
- Values above 25 (men) or 20 (women) may indicate exceptional muscle development
- FFMI is less affected by body fat changes than BMI
- Useful for tracking muscle gain/loss during training
- Monitor trends over time rather than single measurements
- Take measurements at the same time of day for consistency
- Track changes in lean mass during weight loss to preserve muscle
- Use FFMI to assess muscle building progress
- Consider that muscle weighs more than fat by volume
- Combine with progress photos and performance metrics
- Measurements are estimates - DEXA scans provide more accuracy
- Body Fat %: Use if you know your body fat percentage from DEXA, BodPod, or other methods
- Measurements: Calculate body fat using circumference measurements (US Navy method)
- For most accurate results, use professional body fat measurement methods
- Circumference measurements are estimates but useful for tracking trends
- Age is used for muscle mass calculations (Boer formula)
How to Use This Body Fat to Lean Mass Calculator
Our body composition calculator analyzes your lean body mass, fat mass, muscle mass, and Fat-Free Mass Index (FFMI). Here's how to use it:
- Choose your preferred unit system (metric or imperial).
- Select your gender (male or female) for accurate calculations.
- Choose your input method:
- Body Fat %: If you know your body fat percentage from professional testing
- Measurements: To calculate body fat using circumference measurements
- Enter your age, height, and weight.
- If using body fat percentage, enter your known body fat %.
- If using measurements, enter your neck, waist, and hip (for women) circumferences.
The calculator will instantly show your body composition breakdown, including lean mass, fat mass, muscle mass, bone mass, organ mass, BMI, and FFMI with category assessment.
Understanding Body Composition
Body composition analysis provides a detailed breakdown of your body weight into different components, offering insights beyond simple weight or BMI measurements.
Key Components:
- Lean Body Mass (LBM): Total weight minus fat mass, including muscle, bone, organs, and water
- Fat Mass: Total body fat including essential fat (needed for basic functions) and storage fat
- Muscle Mass: Skeletal muscle calculated using the scientifically validated Boer formula
- Bone Mass: Estimated bone weight (approximately 15% for men, 12% for women)
- Organ Mass: Internal organs, blood, and other lean tissue components
Fat-Free Mass Index (FFMI)
FFMI is a more accurate measure than BMI for athletes and muscular individuals, as it accounts for lean body mass relative to height.
FFMI = Lean Body Mass (kg) ÷ Height (m)²FFMI Categories:
| Category | Men | Women | Description |
|---|---|---|---|
| Below Average | <16 | <14 | Lower muscle mass relative to height |
| Average | 16-17 | 14-15 | Typical muscle mass for general population |
| Above Average | 17-18 | 15-16 | Good muscle development |
| Excellent | 18-20 | 16-17 | Well-developed musculature |
| Superior | 20-22 | 17-18 | High level of muscle development |
| Exceptional | 22-25 | 18-20 | Elite level muscle mass |
Input Methods Explained
Body Fat Percentage Method
Use this method if you know your body fat percentage from professional testing such as:
- DEXA scan (most accurate)
- BodPod (air displacement plethysmography)
- Hydrostatic weighing
- Professional bioelectrical impedance analysis
This method provides the most accurate results when you have reliable body fat data.
Measurements Method
This method uses the US Navy circumference formula to estimate body fat percentage from body measurements:
- Neck: Measure just below the Adam's apple, keeping tape level
- Waist: Measure at the narrowest point, usually just above the navel
- Hips (women only): Measure at the widest point of the hips
While less accurate than professional methods, this provides a good estimate and is useful for tracking changes over time.
Tips for Accurate Measurements
- Take measurements at the same time of day for consistency
- Measure on bare skin or over thin clothing
- Keep the measuring tape snug but not tight
- Take multiple measurements and use the average
- Have someone help you measure for better accuracy
- Track trends over time rather than focusing on single measurements
- Consider professional body composition testing for baseline measurements
Using Results for Fitness Goals
Weight Loss Goals
- Monitor lean mass to ensure you're losing fat, not muscle
- Aim to maintain or increase FFMI while reducing body fat
- Track muscle mass changes during caloric restriction
Muscle Building Goals
- Use FFMI to track muscle building progress
- Monitor lean mass increases over time
- Compare your FFMI to category ranges for your gender
Body Recomposition
- Track simultaneous fat loss and muscle gain
- Weight may stay stable while body composition improves
- Focus on lean mass and body fat percentage changes