Lean Body Mass Calculator
Estimate your lean body mass (fat-free mass) using the Boer and Hume formulas. Lean body mass includes muscle, bone, organs, and water — everything except stored fat.
How This Calculator Works
Formula: Boer and Hume Formulas
Lean body mass is estimated using height and weight inputs applied to sex-specific regression equations. The Boer formula (1984) and Hume formula (1966) each use different coefficients to predict fat-free mass. Both provide estimates without requiring body fat measurements or specialized equipment. Results represent total body weight minus estimated fat mass.
Limitations
- These are estimation formulas and may differ from actual lean mass measured by DEXA or other clinical methods.
- Accuracy decreases at extreme body compositions (very lean or very high body fat).
- The formulas do not account for individual variation in bone density or hydration status.
- Results are population-level estimates and may not precisely reflect individual body composition.
These calculations are estimates based on established formulas. Individual results vary. Consult a healthcare professional before making significant changes to your diet or exercise routine.
Lean body mass (LBM) represents the weight of everything in your body except stored fat. This includes skeletal muscle, bones, organs, blood, water, and connective tissue. Understanding your lean body mass can be valuable for setting nutritional targets, especially protein intake, and for tracking body composition changes over time.
This calculator uses two established estimation formulas. The Hume formula, published in 1966, and the Boer formula, published in 1984, both use height and weight to estimate lean mass through sex-specific regression equations. By presenting results from both formulas, you get a range that accounts for methodological differences.
Knowing your lean body mass is particularly useful when calculating protein requirements, as many evidence-based protein recommendations are based on lean mass rather than total body weight. This approach ensures that protein targets scale appropriately regardless of body fat levels.
Lean body mass is also a better indicator of metabolic rate than total body weight. Muscle tissue is metabolically active and burns more calories at rest than fat tissue. Individuals with higher lean mass relative to their total weight typically have higher basal metabolic rates.
For the most actionable results, track lean body mass over time rather than focusing on a single measurement. Increasing lean mass while maintaining or reducing total weight indicates favorable body composition changes. Pair this calculator with the Body Fat Percentage Calculator for a more comprehensive view of your body composition.