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Lean Body Mass Calculator

Lean body mass (LBM) is the total weight of everything in your body except fat — including muscles, bones, organs, water, and connective tissue. Understanding your lean mass helps you set realistic fitness goals, monitor muscle gain or loss during training, and evaluate your body composition more accurately than weight alone. This calculator uses the Boer formula, a well-established estimation method based on your height, weight, and biological sex.

Quick Answer

Lean body mass is everything except fat — muscle, bone, water, and organs. It typically makes up 60–90% of total body weight.

These results are estimates based on general formulas and are not a substitute for professional medical advice. Consult a healthcare provider before making health decisions.

Enter your sex, weight, and height above to calculate your lean body mass.

How the Formula Works

  1. Measure your weight in kilograms. If using pounds, convert by multiplying by 0.453592.

    weight (kg) = weight (lbs) × 0.453592

  2. Measure your height in centimeters. If using feet and inches, convert to centimeters first.

    height (cm) = (feet × 12 + inches) × 2.54

  3. Apply the Boer formula for males: multiply weight by 0.407, add height multiplied by 0.267, then subtract 19.2.

    Males: LBM (kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2

  4. Apply the Boer formula for females: multiply weight by 0.252, add height multiplied by 0.473, then subtract 48.3.

    Females: LBM (kg) = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3

  5. Calculate estimated body fat percentage by subtracting lean mass from total weight, dividing by total weight, and multiplying by 100.

    Body fat % = ((weight − LBM) / weight) × 100

Limitations

  • The Boer formula provides an estimate and cannot account for individual differences in muscle mass, bone density, or hydration levels.
  • Results may be less accurate for individuals at extreme ends of the weight or height spectrum, including very lean athletes or those with obesity.
  • This calculator does not distinguish between different types of lean tissue such as muscle, bone, or organ weight.
  • Age is not factored into the Boer formula, though body composition changes significantly with aging.
  • For the most accurate lean body mass measurement, methods such as DEXA scans or hydrostatic weighing are recommended.

Frequently Asked Questions

What is lean body mass and why does it matter?
Lean body mass (LBM) is your total body weight minus all fat mass. It includes muscle, bone, organs, and water. Tracking LBM helps you understand whether weight changes come from muscle or fat, which is important for fitness progress and overall health assessment.
What is the Boer formula?
The Boer formula is a validated estimation method published in 1984 that calculates lean body mass from height, weight, and biological sex. It uses different coefficients for males and females to account for typical differences in body composition.
How accurate is the Boer formula compared to other methods?
The Boer formula provides a reasonable population-level estimate but is less precise than direct measurement methods like DEXA scans, bioelectrical impedance analysis, or hydrostatic weighing. It is best used as a quick screening tool rather than a clinical measurement.
Can I use this calculator to track muscle gain?
You can use it as a rough indicator of changes over time, but small changes in lean mass may not be reliably detected by a formula-based estimate. For precise muscle-gain tracking, pair this tool with periodic body composition measurements from a healthcare provider.
What is a normal body fat percentage?
Healthy body fat ranges vary by sex and age. For adult males, 10-20% is generally considered healthy, while for adult females, 18-28% is typical. Essential fat (the minimum for physiological function) is about 2-5% for males and 10-13% for females.

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