Lean Body Mass Calculator
Estimate your lean body mass (fat-free weight) using multiple scientifically validated formulas.
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About the Lean Body Mass Calculator
Lean body mass (LBM) is everything in your body that is not fat: your muscle, bone, organs, water and connective tissue. It is the engine of your metabolism and a big part of strength and function, which is why preserving it matters so much during weight loss and aging. This calculator estimates your lean body mass from your height, weight and sex.
I often steer people toward lean body mass because it reframes goals in a healthier direction. Instead of just losing weight, the aim becomes losing fat while protecting the lean tissue that keeps you strong, capable and metabolically active. That mindset tends to produce better, more lasting results.
What lean body mass is
Your weight is made up of fat mass plus lean mass. Lean body mass is that second part: muscle, bone, organs, water and everything else that is not stored fat. Muscle is the component you can most influence, and it is metabolically active, meaning it burns more energy at rest than fat does. Protecting and building it is central to long-term health and a steady metabolism.
How it is estimated
This calculator uses validated formulas (such as the Boer equation) that estimate lean mass from your height, weight and sex. If you know your body fat percentage, lean mass can be derived even more directly as your weight minus your fat mass. Either way it is an estimate, useful for tracking and goal-setting rather than as a precise lab value, so focus on changes over time.
Why it matters for weight loss
When people lose weight too aggressively, a meaningful share of the loss can come from lean tissue, which lowers metabolism and strength, exactly the opposite of what most people want. Knowing your lean body mass helps you aim to keep it steady while fat comes down. The proven tools are enough protein and regular strength training, which together signal your body to hold onto muscle during a deficit.
Protecting lean mass as you age
Lean mass naturally tends to decline with age (a process called sarcopenia), which affects strength, balance and metabolism. The encouraging news is that this is very responsive to action: resistance training and adequate protein at any age help maintain and even rebuild muscle. Tracking lean body mass gives you a tangible reason to keep up those habits, and a way to see them working.
Sources & method
This calculator uses established, peer-reviewed formulas and reference ranges from recognized health and nutrition authorities. Results are estimates for general education, not a medical diagnosis. For decisions about your health, consult a qualified clinician. Reviewed by Macro & Meals Editorial Team, Content editor.
Frequently Asked Questions
Lean body mass is everything in your body that is not fat: muscle, bone, organs, water and connective tissue. Muscle is the part you can most influence, and because it is metabolically active, it burns more energy at rest than fat, making it central to a healthy metabolism.
This calculator uses validated formulas such as the Boer equation, estimating lean mass from your height, weight and sex. If you know your body fat percentage, lean mass can also be derived as your weight minus your fat mass. It is an estimate best used for tracking change over time.
Losing weight too aggressively can strip away lean tissue, lowering your metabolism and strength, the opposite of most people's goals. Keeping lean mass steady while fat comes down, through enough protein and regular strength training, leads to better and more lasting results.
Regular resistance training combined with adequate protein is the proven approach, signaling your body to build and keep muscle. This works at any age and is especially valuable later in life, when lean mass naturally tends to decline. Consistency matters more than intensity.
