Lean Body Mass Calculator Formula
Understand the math behind the lean body mass calculator. Each variable explained with a worked example.
Formulas Used
Lean Body Mass (lbs)
lean_mass_lbs = weight_lbs * (1 - body_fat_pct / 100)Lean Body Mass (kg)
lean_mass_kg = weight_lbs * (1 - body_fat_pct / 100) * 0.453592Fat Mass (lbs)
fat_mass_lbs = weight_lbs * body_fat_pct / 100Variables
| Variable | Description | Default |
|---|---|---|
weight_lbs | Body Weight(lbs) | 180 |
body_fat_pct | Body Fat Percentage(%) | 20 |
How It Works
Lean Body Mass Formula
Lean Body Mass = Weight x (1 - Body Fat % / 100)
Lean body mass includes everything except fat: muscles, bones, organs, water, and other tissues.
Worked Example
A 180 lb person with 20% body fat.
- 01Lean mass = 180 x (1 - 20/100) = 180 x 0.80 = 144 lbs
- 02In kg = 144 x 0.4536 = 65.3 kg
- 03Fat mass = 180 x 0.20 = 36.0 lbs
Frequently Asked Questions
What is lean body mass?
Lean body mass is your total body weight minus fat mass. It includes muscle, bone, organs, and water.
Why is lean body mass important?
It helps determine calorie needs more accurately than total weight and is useful for tracking body composition changes.
Learn More
Guide
Body Fat Percentage Guide: How to Measure and Interpret Your Results
Learn how to measure body fat percentage, what healthy ranges look like for men and women, and how different measurement methods compare in accuracy and practicality.
Ready to run the numbers?
Open Lean Body Mass Calculator