Body composition calculator
Lean Body Mass Calculator
Calculate lean body mass and fat mass from your body weight and estimated body fat percentage.
Lean body mass is the number FFMI starts with. If you do not know your body fat percentage yet, use the Body Fat Calculator first.
LBM
Lean body mass
Fat
Estimated fat mass
FFMI
Use result next
LBM Calculator
Your Lean Body Mass
Uses body weight and body fat percentage.
Runs in your browser. No account required.
Guide
How the Lean Body Mass Calculator Works
Lean body mass is your body weight minus estimated fat mass. It includes muscle, bone, organs, water, connective tissue, and other fat-free tissue.
The formula is simple: Lean Body Mass = body weight × (1 - body fat percentage). Fat Mass = body weight × body fat percentage.
For example, if someone weighs 90 kg and has 20% body fat, estimated lean body mass is 72 kg and estimated fat mass is 18 kg.
Why LBM Matters for FFMI
FFMI uses lean body mass, not total body weight. That is why a better body fat estimate can make your FFMI result more useful. Once you know your lean mass estimate, use the FFMI calculator to compare it relative to your height.
Frequently Asked Questions
What is lean body mass?
Lean body mass is everything in your body except fat mass. It includes muscle, organs, water, bone, and connective tissue.
Is lean body mass the same as fat-free mass?
For everyday calculator use, lean body mass and fat-free mass are often used the same way: body weight minus fat mass.
Why does body fat accuracy matter?
Because lean body mass is calculated from body fat percentage. If the body fat estimate is off, the lean mass result will also be off.