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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.

Reviewed by GetHealthyCalculators Editorial Team · Updated April 14, 2026

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 very lean athletes, individuals with obesity, the very tall or very short, or people with edema or fluid-shift conditions.
  • This calculator does not distinguish between different types of lean tissue — muscle, bone, connective tissue, or organ weight.
  • Age is not factored into the Boer formula, though body composition changes materially with aging (sarcopenia and visceral fat gain).
  • Hydration status can shift apparent lean mass by 1–3 kg day to day — fasting and well-rested conditions give the most consistent readings.
  • For accurate clinical measurement, DXA, air-displacement plethysmography (BOD POD), or hydrostatic weighing remain the reference methods.

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.
How does lean body mass change with age?
After age 30, sedentary adults lose roughly 3–8% of lean mass per decade (sarcopenia). The EWGSOP2 consensus (Cruz-Jentoft, Age & Ageing 2019) defines clinically relevant sarcopenia by low muscle strength plus low muscle quantity or quality. Resistance training and adequate protein (1.0–1.2 g/kg/day or higher) can slow that decline.
How often should I retest my lean body mass?
Every 4–8 weeks is a reasonable cadence during active training or dieting. More frequent measurements add noise. Always measure under similar conditions — fasted, well-hydrated, at the same time of day.
Does lean body mass tell me my muscle mass specifically?
No. Lean body mass includes muscle, bone, water, organs, and connective tissue. Skeletal muscle mass is a subset — roughly 40–50% of LBM in healthy adults. DXA, MRI, or D3-creatine dilution tests are needed to isolate skeletal muscle mass clinically.
When should I consult a clinician about lean body mass?
If you are losing lean mass despite adequate protein and training, experiencing unexplained weight loss, or screening for sarcopenia after age 65, talk with your primary-care physician or a registered dietitian. Grip strength, gait speed, and DXA can provide clinical confirmation.

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