Lean Body Mass Calculator
Adjust the inputs below. Results update as you type.
How it works
LBM = total weight × (1 − body fat%). Boer formula (men): LBM = 0.407W + 0.267H − 19.2; women: 0.252W + 0.473H − 48.3. Used for drug dosing, anesthesia, and fitness tracking. Increasing LBM raises BMR since muscle burns more calories at rest than fat. Track LBM (not just weight) to distinguish fat loss from muscle loss during a diet.
Input guidance
- Use measured values (recent weight, height, activity level) rather than guesses.
- Recalculate every few weeks as your routine and body metrics change.
- Pair screening metrics with context such as sleep, stress, and medical history.
The formula
Lean body mass = total weight − fat mass = weight × (1 − body fat percentage). The Boer formula also estimates LBM from height and weight directly.
Worked example
A 180 lb person at 20% body fat has fat mass of 36 lb and lean body mass of 144 lb.
More examples to test
- Maintenance case: keep activity constant and observe expected baseline ranges.
- Adjustment case: change only one major variable to understand sensitivity.
How to interpret results
Use results for awareness and planning, then validate with qualified medical or nutrition professionals for individualized decisions.
When this can be inaccurate
Population formulas cannot account for all biological factors such as medical conditions, medication effects, body composition differences, and genetics.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
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General wellness resource.
Frequently asked questions
What is lean body mass?+
Everything in your body that is not fat: muscle, bone, organs, and water. It is a key reference for nutrition and medication dosing.
Why does LBM matter?+
It drives your metabolic rate and strength. Preserving lean mass during weight loss keeps metabolism higher and results healthier.
How do I increase lean mass?+
Resistance training plus adequate protein and calories. Gaining muscle is slow but raises strength and resting energy use.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.