Lean Body Mass Calculator Formula

Understand the math behind the lean body mass calculator. Each variable explained with a worked example.

Use the Lean Body Mass Calculator

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) * 0.453592

Fat Mass (lbs)

fat_mass_lbs = weight_lbs * body_fat_pct / 100

Variables

VariableDescriptionDefault
weight_lbsBody Weight(lbs)180
body_fat_pctBody 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.

weight_lbs = 180body_fat_pct = 20
  1. 01Lean mass = 180 x (1 - 20/100) = 180 x 0.80 = 144 lbs
  2. 02In kg = 144 x 0.4536 = 65.3 kg
  3. 03Fat mass = 180 x 0.20 = 36.0 lbs

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