Lean Body Mass
Free Lean Body Mass for health & fitness. Enter your measurements for personalized results with clear explanations and reference ranges.
Formula
LBM = 0.407 × weight + 0.267 × height - 19.2 (Boer, male)
Lean body mass is calculated using validated formulas based on height and weight, or directly from body fat percentage if known. Multiple formulas exist for comparison.
Worked Examples
Example 1: Using Body Fat Percentage
Problem:Male, 85kg with 18% body fat. Calculate lean body mass.
Solution:When body fat % is known:\nLBM = Total Weight × (1 - Body Fat %)\nLBM = 85 × (1 - 0.18)\nLBM = 85 × 0.82\nLBM = 69.7 kg\n\nFat Mass = 85 - 69.7 = 15.3 kg\n\nThis is the most accurate method when you know your body fat percentage.
Result:69.7 kg lean mass, 15.3 kg fat mass
Example 2: Using Boer Formula
Problem:Female, 165cm, 60kg, body fat unknown.
Solution:Boer Formula (Female):\nLBM = 0.252 × Weight + 0.473 × Height - 48.3\nLBM = 0.252 × 60 + 0.473 × 165 - 48.3\nLBM = 15.12 + 78.05 - 48.3\nLBM = 44.87 kg\n\nEstimated Fat = 60 - 44.87 = 15.13 kg\nEstimated Body Fat % = 15.13/60 × 100 = 25.2%
Result:44.9 kg lean mass (estimated)
Example 3: Lean Mass Index Calculation
Problem:Male, 180cm, lean mass calculated as 65kg.
Solution:Lean Mass Index = LBM / Height²\nHeight in meters = 1.80m\n\nLMI = 65 / (1.80)²\nLMI = 65 / 3.24\nLMI = 20.1 kg/m²\n\nNormal male LMI range: 16-20 kg/m²\nThis person is at the upper end of normal, indicating good muscle mass for their height.
Result:LMI = 20.1 kg/m² (good muscle mass)
Frequently Asked Questions
What is lean body mass?
Lean body mass (LBM) is your total body weight minus fat mass. It includes muscles, bones, organs, skin, blood, and water - essentially everything except stored fat. LBM is also called fat-free mass (FFM), though technically FFM excludes essential fat while LBM includes it.
Why is lean body mass important?
LBM is crucial for: 1) Metabolism - muscle burns more calories than fat at rest, 2) Strength and physical function, 3) Medical dosing - many drugs are dosed based on LBM rather than total weight, 4) Fitness goals - helps track if you're gaining muscle vs fat, 5) Identifying sarcopenia (muscle loss) in elderly.
What's the difference between lean mass and muscle mass?
Lean mass includes ALL non-fat tissue: muscles, bones, organs, blood, water, etc. Muscle mass is only the weight of skeletal muscles. Skeletal muscle typically comprises about 40-50% of lean mass in healthy adults. You can't directly measure muscle mass without advanced imaging.
What is Lean Mass Index (LMI)?
LMI is lean mass divided by height squared (like BMI but for lean mass only). Normal LMI is roughly 16-20 kg/m² for men and 14-18 kg/m² for women. Low LMI may indicate sarcopenia. Athletes typically have higher LMI due to greater muscle mass.