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Lean Body Mass

Calculate your fat-free weight
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Your Lean Body Mass
0 lbs
Body Fat Mass: 0 lbs

What is Lean Body Mass (LBM)?

If you stepped on a scale, subtracted all of your body fat, and weighed what was left, that number would be your Lean Body Mass (LBM).

Often called "Fat-Free Mass," this metric includes:

  • Muscle Tissue
  • Bones & Skeletal Structure
  • Organs (Heart, Liver, Brain)
  • Blood & Water

LBM is a superior metric to Total Weight because it tracks the "Good Weight." If your total weight drops but your LBM stays the same, you know you successfully lost pure fat.

The Boer Formula vs. Body Fat Method

Our calculator offers two ways to find your number. Which one should you use?

1. The Body Fat Method (Best)

If you have already used calipers or our Body Fat Calculator, use the "Known Body Fat" tab. This is the most precise mathematical way to determine LBM.

Equation: Total Weight - (Total Weight × BF%)

2. The Boer Formula (Estimation)

If you don't know your body fat percentage, the Boer Formula is the medical standard for estimation. Developed in 1984, this formula predicts LBM based on your height and weight statistics.

Did You Know? Anesthesiologists use the Boer Formula to calculate dosage for surgery. Since fat tissue doesn't absorb drugs the same way muscle does, knowing LBM prevents overdosing in obese patients.

Why Bodybuilders Obsess Over LBM

In the fitness world, LBM is used to calculate your FFMI (Fat-Free Mass Index).

While BMI punishes muscle (classifying muscular people as obese), FFMI rewards muscle. Knowing your LBM helps you set realistic bulking goals. A natural lifter can typically only gain 20-30 lbs of LBM above their baseline in their entire career.

Water Weight Fluctuations

Important Note: Since LBM includes Water, it can fluctuate daily.

  • Creatine: Taking creatine pulls water into the muscles, increasing your LBM. This is "good" weight.
  • Low Carb Diets: Cutting carbs depletes glycogen (and the water attached to it). This causes a rapid drop in LBM on the scale, even though you didn't lose muscle tissue.

Your Composition Toolkit

💪 Body Fat % 🎯 Ideal Weight 🥩 Protein for LBM