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Body Fat to Lean Mass Calculator

Calculate lean body mass, fat mass, muscle mass, and body composition analysis for tracking fitness progress.

Gender
Input Method
years
cm
kg
%
15.0%
24.2

Body Composition

Lean Body Mass: 59.5 kg
Fat Mass: 10.5 kg
Muscle Mass: 54.7 kg
Bone Mass: 10.5 kg
Organ Mass: -5.7 kg

Fat-Free Mass Index (FFMI)

FFMI: 20.6
Category: Superior

FFMI Ranges (Men)

Below Average: <16
Average: 16-17
Above Average: 17-18
Excellent: 18-20
Superior: 20-22
Exceptional: 22-25
Understanding Body Composition

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.

Fat-Free Mass Index (FFMI)
  • 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
Tracking Body Composition Changes
  • 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
Input Methods
  • 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:

  1. Choose your preferred unit system (metric or imperial).
  2. Select your gender (male or female) for accurate calculations.
  3. Choose your input method:
    • Body Fat %: If you know your body fat percentage from professional testing
    • Measurements: To calculate body fat using circumference measurements
  4. Enter your age, height, and weight.
  5. If using body fat percentage, enter your known body fat %.
  6. 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)²

FFMI Categories:

CategoryMenWomenDescription
Below Average<16<14Lower muscle mass relative to height
Average16-1714-15Typical muscle mass for general population
Above Average17-1815-16Good muscle development
Excellent18-2016-17Well-developed musculature
Superior20-2217-18High level of muscle development
Exceptional22-2518-20Elite 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