Lean Body Mass Calculator

Lean body mass (LBM) represents everything in your body that is not fat: muscles, bones, organs, water, and connective tissue. Knowing your LBM helps you set protein targets, track muscle gain, and evaluate body-composition changes more accurately than weight alone.

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Understanding Lean Body Mass

Lean body mass (LBM) is your total body weight minus all fat weight. It includes skeletal muscle, bone, water, blood, organs, and connective tissue. LBM is a critical metric for athletes, dieters, and anyone interested in body recomposition because it tells you how much metabolically active tissue you carry. A higher LBM generally correlates with a higher basal metabolic rate, meaning you burn more calories at rest.

Tracking LBM over time is more informative than tracking total weight. If your weight stays the same but your LBM rises, you are successfully gaining muscle while losing fat, a phenomenon known as body recomposition.

Estimation Formulas

Boer Formula (1984)

  • Men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2
  • Women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3

James Formula (1976)

  • Men: LBM = 1.1 × weight (kg) − 128 × (weight / height)2
  • Women: LBM = 1.07 × weight (kg) − 148 × (weight / height)2

Why LBM Matters for Nutrition

Protein recommendations for athletes are often given per kilogram of lean body mass rather than total weight. A common guideline is 1.6-2.2 g of protein per kg of LBM per day for those engaged in resistance training. Knowing your LBM lets you calculate a precise protein target that accounts for your actual muscle tissue rather than including fat mass.

Limitations

Estimation formulas use height and weight as proxies and do not directly measure muscle tissue. Their accuracy can vary significantly for obese individuals, very lean athletes, and those with atypical body proportions. For a clinical-grade measurement, consider DEXA or bioelectrical impedance analysis. Always pair LBM estimates with other metrics for a holistic view of your health.

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Frequently Asked Questions

What is a good lean body mass percentage?
For men, a lean body mass of 75-85% of total weight is common among fit individuals, while women typically range from 68-78%. Elite athletes may have even higher lean mass percentages. The ideal value depends on your sport, goals, and overall health.
How do I increase my lean body mass?
Progressive resistance training is the most effective way to increase LBM. Combine strength training with adequate protein intake (1.6-2.2 g/kg of LBM) and sufficient calories to support muscle growth. Sleep and recovery are also essential for muscle protein synthesis.
Is lean body mass the same as muscle mass?
Not exactly. Lean body mass includes everything that is not fat: muscles, bones, organs, water, and connective tissue. Skeletal muscle makes up the largest component of LBM, but the two terms are not interchangeable. Muscle mass is a subset of lean body mass.
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