Lean Body Mass Calculator | OmniCalculator

  • Adam
  • November 1, 2025

Free lean body mass calculator using Boer, James, Hume, and Peters formulas. Calculate your fat-free mass and body composition breakdown.

💪 🦵 💪

Lean Body Mass Calculator

Calculate your lean body mass using multiple formulas. Find what percentage of your body weight is muscle, bone, and organs.

📋 Quick Navigation

💪 Calculate your lean body mass and body composition! 🦵
in cm (100-250)
in kg (30-300)
for children formula option
Choose calculation formula
in kg
your measured body fat %
Lean Body Mass (LBM)
0 kg
Estimated lean mass

Total Weight

75
kg

Lean Mass

60
kg

Body Fat

15
kg

LBM %

80%
of total weight

📊 Formula Results

Formula Lean Body Mass Body Fat % LBM %
Boer 0 kg 0% 0%
James 0 kg 0% 0%
Hume 0 kg 0% 0%

🧮 Lean Body Mass Formulas

Boer Formula (Most Accurate)

Developed through medical research, the Boer formula is widely considered the most accurate for adult LBM estimation. It accounts for weight and height differences between genders.

For Men:
eLBM = 0.407 × Weight (kg) + 0.267 × Height (cm) - 19.2

For Women:
eLBM = 0.252 × Weight (kg) + 0.473 × Height (cm) - 48.3

Example: 75 kg male, 180 cm tall
eLBM = 0.407 × 75 + 0.267 × 180 - 19.2
eLBM = 30.525 + 48.06 - 19.2 = 59.385 kg

James Formula

Another accurate formula for adults, using BMI-like calculations. Often gives results close to Boer but may vary for extremes of height.

For Men:
eLBM = 1.1 × Weight (kg) - 128 × (Weight ÷ Height)²

For Women:
eLBM = 1.07 × Weight (kg) - 148 × (Weight ÷ Height)²

Hume Formula

A modification of earlier equations, Hume formula provides another perspective on LBM estimation. Results typically fall between Boer and James.

For Men:
eLBM = 0.32810 × Weight (kg) + 0.33929 × Height (cm) - 29.5336

For Women:
eLBM = 0.29569 × Weight (kg) + 0.41813 × Height (cm) - 43.2933

Peters Formula (Children ≤14)

For children aged 14 and younger, body composition changes dramatically with growth. Peters formula uses a different approach based on extracellular volume.

Step 1: Calculate eECV
eECV = 0.0215 × Weight (kg)^0.6469 × Height (cm)^0.7236

Step 2: Calculate eLBM
eLBM = 3.8 × eECV

Body Fat Percentage Method (Most Accurate)

If you know your body fat percentage (from DEXA, hydrostatic weighing, or other measurement), this formula is exact:

LBM = Total Weight × (1 - Body Fat %)

Example: 75 kg person with 20% body fat
LBM = 75 × (1 - 0.20)
LBM = 75 × 0.80 = 60 kg

📊 Understanding Body Composition

What is Lean Body Mass?

Lean Body Mass (LBM) is everything in your body except fat tissue. This includes skeletal muscle, bones, organs, connective tissue, water, and blood. LBM is metabolically active - it burns calories even at rest.

Body Composition Breakdown

Total body weight = Lean Body Mass + Body Fat Mass. For example, a 75 kg person with 20% body fat has:

  • Lean Body Mass: 60 kg (80%)
  • Body Fat: 15 kg (20%)

Healthy LBM Ranges

Healthy LBM as percentage of total weight typically ranges from 60-90%, depending on gender and fitness level:

  • Men: 75-90% LBM is typical (10-25% body fat)
  • Women: 70-85% LBM is typical (15-30% body fat)
  • Athletes: Often 85-95% LBM (5-15% body fat)
  • Sedentary: May be 60-75% LBM (25-40% body fat)

Why LBM Matters

Medical Use: Dosages for water-soluble medications are calculated based on LBM rather than total weight. Fitness: LBM determines metabolic rate - more muscle burns more calories. Performance: Athletes track LBM to monitor muscle gains separate from fat changes.

💡 Important: Two people with the same weight can have very different body compositions. A muscular athlete and a sedentary person at the same weight have different LBM values due to different muscle-to-fat ratios!

📐 Comparison of Methods

Formula Method vs Body Fat Method

Formula Method: Uses only height, weight, and gender. Good for quick estimation. Results average ±3-5 kg. Body Fat Method: Requires knowing body fat percentage. Most accurate if body fat is measured accurately. Perfect calculation if input is correct.

How to Measure Body Fat

DEXA (Most Accurate): Medical imaging, ±2% accuracy. Hydrostatic Weighing: Water displacement, ±2-3% accuracy. Bioelectrical Impedance: Portable devices, ±3-5% accuracy. Skin Calipers: Manual measurement, ±3-6% accuracy. Visual/Photos: Very rough estimate, ±10%+ accuracy.

Which Formula to Use?

  • For most people: Use Boer formula (default)
  • For verification: Average all three adult formulas
  • For children ≤14: Use Peters formula
  • For extreme heights: James or Hume may work better
  • Most accurate: Know your body fat % and use simple formula

Factors Affecting LBM

  • Gender: Men naturally have more LBM
  • Age: LBM decreases with age (~3-8% per decade after 30)
  • Training: Strength training increases muscle LBM
  • Genetics: Muscle-building potential varies
  • Hormones: Testosterone, thyroid, growth hormone affect LBM

❓ Frequently Asked Questions

Is lean body mass the same as muscle mass? +
No! Lean body mass includes much more than just muscle. It's all non-fat tissue: muscles, bones, organs, blood, water, skin, and connective tissue. Skeletal muscle is only part of LBM, typically 30-40% of total body weight.
Why do formulas give different results? +
Different formulas were developed using different research populations and methodologies. Boer uses one population, James another, Hume a third. They use different coefficients and calculations. Averaging multiple formulas gives a better estimate than relying on one. Differences are typically within 2-3 kg.
Can I increase my lean body mass? +
Yes! Primarily by building muscle through strength training combined with adequate protein intake. You can also maintain or increase bone density through weight-bearing exercise. Losing body fat while maintaining muscle increases LBM percentage. Hormones, sleep, and stress management also affect LBM.
Why is LBM important for medical dosing? +
Many water-soluble medications don't penetrate fat tissue. Using total body weight can lead to overdosing in obese patients. Water-soluble drugs distribute in lean mass and water, not fat. Using LBM for dosing ensures correct medication levels regardless of body composition.
Does age affect lean body mass? +
Yes significantly! LBM peaks in the 20s-30s, then gradually decreases about 3-8% per decade after age 30 due to sarcopenia (age-related muscle loss). This is why older adults need more strength training. However, active older adults can maintain higher LBM than sedentary younger people!
How accurate are these LBM estimates? +
Formulas are typically accurate within ±3-5 kg for most people. The body fat percentage method is exact if your body fat percentage is measured accurately. Accuracy decreases for extreme heights, very muscular individuals, or very obese individuals. Use these as estimates, not exact measurements!
Should athletes use different calculations? +
Athletes with very high muscle mass may get better results knowing their actual body fat percentage and using the body fat method. The formulas assume average body composition, so highly muscular individuals might have higher actual LBM than formulas estimate. Consider bioelectrical impedance or DEXA for athletes.
How does LBM relate to metabolism? +
LBM is metabolically active tissue that burns calories at rest. More muscle = higher resting metabolic rate (RMR). This is why building muscle is effective for weight loss - you burn more calories even sleeping! Each kg of muscle burns roughly 6-10 kcal per day at rest.

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