Compute your estimated lean body mass (LBM) using the Boer, James, Hume, and Peters formulas for adults and children.
Lean Body Mass vs. Fat Free Mass
Although often used interchangeably, Lean Body Mass (LBM) and Fat Free Mass (FFM) represent distinct body composition metrics:
• Lean Body Mass (LBM) includes the weight of bones, skeletal muscle, water, ligaments, tendons, internal organs, and the **essential fat** stored inside organs (which protects tissue and carries vital hormones).
• Fat Free Mass (FFM) represents the total weight of the body minus **all fat weight**, including essential fats. FFM is strictly the weight of fat-free tissues only.
Subtracting essential fats from LBM results in a 2% to 3% difference in men and a 5% to 12% difference in women.
Clinical & Health Significance of Lean Body Mass
Nutritional & Hospital Screening
Under the Global Leadership Initiative on Malnutrition (GLIM), a decline in muscle mass (the primary part of LBM) is a diagnostic criterion for malnutrition in clinical care.
Metabolic Rate & Insulin Sensitivity
Lean muscle is highly active tissue. Higher LBM increases your Basal Metabolic Rate (BMR), helping regulate blood sugar, improve insulin sensitivity, and protect against type 2 diabetes.
Preventing Sarcopenia
Aging causes a natural decline in LBM (known as sarcopenia). Monitoring LBM helps track strength, preserve mobility, and lower the risk of falls in older adults.
The Lean Mass Index (LMI) Alternative to BMI
Traditional Body Mass Index (BMI) often misclassifies muscular athletes as "overweight" or individuals with low muscle mass and high body fat as "healthy." To address this, clinicians use the Lean Mass Index (LMI), calculated as:LMI = Lean Body Mass (kg) / Height (m)²LMI isolates structural lean weight from fat tissue, offering a precise assessment of physical fitness and structural health during weight loss programs.
Formula Reference (Height & Weight Parameters)
In the equations below, W represents weight in kilograms (kg) and H represents height in centimeters (cm):
• Females: LBM = 0.252 × W + 0.473 × H - 48.3
• Females: LBM = 1.07 × W - 148 × (W / H)²
• Females: LBM = 0.29569 × W + 0.41813 × H - 43.2933
• eECV = 0.0215 × W^0.6469 × H^0.7236
• LBM = 3.8 × eECV
1. Boer P. "Estimated lean body mass as an index for normalization of body fluid volumes in man." Am J Physiol 1984; 247: F632-5
2. James, W. "Research on obesity: a report of the DHSS/MRC group." HM Stationery Office 1976
3. Hume, R. "Prediction of lean body mass from height and weight." J Clin Pathol. 1966 Jul; 19(4):389-91.
4. Peters, A. M., Snelling, H. L. R., Glass, D. M., et al. "Estimation of lean body mass in children." British Journal of Anaesthesia 106(5): 719-23 (2011).
How it Works & Formula
Calculates the weight of your body excluding all fat mass, representing muscle, bones, and organs (Boer Formula).
Practical Examples
A male weighing 80 kg and 180 cm tall has an estimated lean body mass of 61.4 kg.
Frequently Asked Questions
What is lean body mass (LBM)?
Lean body mass represents the difference between total body weight and all body fat weight. It includes the weight of bones, muscles, organs, blood, skin, and water.
What is the difference between lean body mass and fat-free mass?
Lean body mass includes essential fats found in internal organs (which protect and cushion them). Fat-free mass subtracts all fat mass including essential fat, resulting in a 2-3% difference in men and 5-12% in women.
How is LBM used in medicine?
The dosage of certain water-soluble anesthetics and specific clinical tests are routinely based on LBM rather than total body weight to prevent overdosing.