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 Calculator
Your Lean Body Mass
Uses body weight and body fat percentage · Free · No sign-up
Guide
Lean Body Mass Formula Example
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 (198 lb) and has 20% body fat, fat mass is 18 kg (40 lb) and lean body mass is 72 kg (159 lb).
Example
Weight: 90 kg (198 lb)
Body fat: 20%
Fat mass: 18 kg (40 lb)
Lean body mass: 72 kg (159 lb)
Formula
Lean body mass = body weight × (1 - body fat %). The better your body fat estimate, the more useful the result.
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 muscle mass?
No. Muscle is only one part of lean body mass. Lean body mass also includes water, bone, organs, and other fat-free tissue.
Why does body fat percentage matter?
Lean body mass is calculated from body fat percentage. If the body fat estimate is too high or too low, the lean mass estimate changes too.
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.