Lean Body Mass Calculator
Calculate your lean body mass using validated Boer and James formulas, or from body fat percentage. Understand your muscle and fat composition. Free, instant.
All calculations run instantly in your browser. No data is sent to any server.
Disclaimer: Results are for informational purposes only and do not constitute medical advice, diagnosis, or treatment. Consult a qualified healthcare professional for personal guidance.
Why Lean Body Mass Matters
LBM is the foundation of metabolic health. Muscle is the primary site of glucose uptake (via GLUT4 transporters), so higher LBM improves insulin sensitivity and reduces type 2 diabetes risk. LBM also determines resting metabolic rate — more muscle means more calories burned at rest. Preserving LBM during weight loss prevents the metabolic adaptation ("starvation mode") that makes weight regain more likely.
Formulas Used
Boer (1984): Men: (0.407 × weight kg) + (0.267 × height cm) − 19.2. Women: (0.252 × weight kg) + (0.473 × height cm) − 48.3. James (1976): Men: 1.1 × weight − 128 × (weight/height)². Women: 1.07 × weight − 148 × (weight/height)². If body fat % is provided, the direct calculation (weight × (1 − bf%/100)) is shown as the most accurate method.
FAQs
What is lean body mass?
Total weight minus fat. Includes muscle, bone, organs, and water. The metabolically active mass that drives BMR, strength, and protein needs.
Most accurate method?
Enter body fat % for the most accurate estimate. DEXA scan is the gold standard. Formula estimates have ±3–4 kg error.