Lean Body Mass
Free Lean Body Mass for health & fitness. Enter your measurements for personalized results with clear explanations and reference ranges.
Medical disclaimer: This calculator is provided for educational and informational purposes only and does not constitute medical advice, diagnosis, or treatment. Results are general estimates and may not reflect your individual circumstances. Always consult a qualified healthcare professional before making decisions about your health.
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: LBM = Total Weight × (1 - Body Fat %) LBM = 85 × (1 - 0.18) LBM = 85 × 0.82 LBM = 69.7 kg Fat Mass = 85 - 69.7 = 15.3 kg This 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): LBM = 0.252 × Weight + 0.473 × Height - 48.3 LBM = 0.252 × 60 + 0.473 × 165 - 48.3 LBM = 15.12 + 78.05 - 48.3 LBM = 44.87 kg Estimated Fat = 60 - 44.87 = 15.13 kg Estimated 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 Height in meters = 1.80m LMI = 65 / (1.80)² LMI = 65 / 3.24 LMI = 20.1 kg/m² Normal male LMI range: 16-20 kg/m² This 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.
How do the different LBM formulas compare?
Boer formula is generally most accurate for average populations. James formula works well for normal BMI ranges. Hume formula is older but still commonly used. All are estimates with 2-5% error margins. If you know your body fat %, calculating LBM directly from that is more accurate.
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.
Can I increase my lean body mass?
Yes, through resistance training combined with adequate protein intake (1.6-2.2g per kg body weight). Muscle growth requires progressive overload, sufficient calories, and recovery time. Beginners can gain 0.5-1 kg of muscle per month; trained individuals gain less. Cardio alone doesn't significantly increase LBM.
Does lean body mass decrease with age?
Yes, sarcopenia (age-related muscle loss) begins around age 30, accelerating after 60. Without intervention, adults lose 3-8% of muscle mass per decade after 30. Resistance training can significantly slow or reverse this decline, maintaining strength and independence in older age.
What's the relationship between LBM and metabolism?
Lean mass is the primary driver of resting metabolic rate (RMR). Each kg of muscle burns roughly 13-15 calories per day at rest. More lean mass = higher metabolism. This is why building muscle helps with weight management and why crash diets that sacrifice muscle are counterproductive.
Should I track lean mass or body fat percentage?
Both are valuable. Body fat % tells you composition ratio; lean mass tells you absolute muscle/organ mass. When losing weight, track both to ensure you're losing fat not muscle. When bulking, ensure lean mass increases faster than fat. Together they give the complete picture.
What is body composition and why is it better than BMI alone?
Body composition describes what your body is actually made of: skeletal muscle, fat mass, bone mineral density, and water. Unlike BMI — which divides weight by height squared and cannot distinguish a pound of muscle from a pound of fat — body composition identifies whether weight is metabolically active tissue or stored energy. Healthy body fat percentages vary by sex and age: for women, 20-32% is generally considered healthy; for men, 8-19%. Measurement methods include DEXA scans (most accurate, ±1-2%), hydrostatic weighing, Bod Pod air displacement, bioelectrical impedance (consumer scales, ±3-5%), and skinfold calipers. A muscular person with a BMI of 27 (overweight) might have excellent body composition, while a sedentary person with a normal BMI could have metabolically risky visceral fat levels.