Health and fitness tools
Lean Body Mass Calculator
Estimate lean body mass from height, weight, age, and sex using Boer, James, and Hume formulas, or calculate from weight and body fat percentage locally in your browser.
Estimate your lean body mass with multiple formulas.
Choose between two methods: formula-based or body fat percentage. The formula method uses three established equations (Boer, James, and Hume) with your age, sex, height, and weight to estimate lean body mass and body fat percentage. The body fat method calculates lean mass directly from weight and body fat percentage: LBM = weight × (1 − body fat % ÷ 100). Metric (cm, kg) and imperial (in, lb) units are supported. These are general estimates for adults; individual factors like muscle mass, bone density, and hydration affect actual values. This is not medical advice; consult a healthcare professional for clinical decisions. All calculations run locally in your browser; your values are not uploaded or stored.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How does the lean body mass calculator work?
The calculator offers two methods. The formula method uses three published equations with your age, sex, height, and weight: Boer (1984), James (1976), and Hume (1966). Each was derived from different study populations. The calculator reports all three results, their average, and the implied body fat percentage from the average LBM. The body fat method computes LBM directly: LBM = weight × (1 − body fat % ÷ 100).
What is lean body mass?
Lean body mass (LBM) is your total body weight minus fat mass. It includes muscle, bones, organs, water, and other non-fat tissues. LBM is typically 60–85% of body weight for women and 75–90% for men, depending on fitness level, age, and body composition. It is used to estimate protein needs, drug dosing, and nutritional status.
Why are there three different formulas?
Boer, James, and Hume each used different reference populations and measurement techniques. Boer (1984) used total body water measurements, James (1976) used body density, and Hume (1966) used cadaver studies. They can differ by several kilograms for the same person. The calculator shows all three so you can see the range; the average is often used as a single estimate.
Can I use this for children or older adults?
These formulas were developed for adults and are not validated for children or adolescents. For older adults, results may be less accurate due to age-related changes in body composition, hydration, and bone density. Always interpret results with clinical context.
Is this a medical measurement or advice?
No. These formulas are population-based estimates and do not account for individual variation in muscle mass, bone density, hydration, or clinical conditions. Results are for educational and planning purposes only. For medical, nutritional, or dosing decisions, consult a qualified healthcare professional using validated methods. All calculations run locally in your browser and are not uploaded or stored.