Estimate your lean body mass (everything that isn't fat) and your fat mass from your height and weight, or directly from your body fat percentage.
What Is Lean Body Mass?
Lean body mass (LBM) is your total body weight minus your fat mass — it includes muscle, bone, organs, water, and connective tissue. Knowing your LBM helps you set protein targets, track muscle gain or loss, and judge progress beyond what the scale alone shows.
How It's Calculated
If you know your body fat percentage, LBM is simply weight × (1 − body fat %). If you don't, this calculator uses the Boer formula, which estimates LBM from your height, weight, and gender. Enter a body fat percentage for a more accurate result, or leave it at 0 to use the estimate.
Why Lean Body Mass Matters
Your LBM drives your resting metabolism — more lean mass means you burn more calories at rest. It's also the basis for protein recommendations and a better progress marker than body weight, since you can lose fat and gain muscle while the scale barely moves.
Using LBM to Track Progress
During a fat-loss phase, the goal is to lose fat mass while keeping LBM stable. During a muscle-building phase, you want LBM to rise. Re-measure every few weeks under similar conditions to see whether changes in your weight are coming from fat or lean tissue.
Tip: For the most accurate result, enter a measured body fat percentage (from calipers, a DEXA scan, or a smart scale). The Boer formula estimate is a solid starting point when you don't have one.
Frequently Asked Questions
What is a good lean body mass?
There's no single 'good' number — it depends on height, frame, and training. More useful is your body fat percentage: roughly 10–20% for men and 18–28% for women is considered healthy. Track whether your LBM holds or rises over time.
How do I calculate lean body mass?
If you know your body fat percentage, multiply your weight by (1 minus that percentage). For example, 180 lb at 20% fat gives 144 lb of lean mass. Without a body fat reading, this calculator uses the Boer formula based on height and weight.
What's the difference between lean body mass and muscle mass?
Lean body mass includes muscle plus bone, organs, and water, so it's larger than muscle mass alone. Skeletal muscle is typically about 40–50% of lean body mass. LBM is easier to estimate, which is why it's the common training metric.
Can I increase my lean body mass?
Yes. Resistance training combined with adequate protein and enough calories builds muscle, the main driver of LBM gains. Progress is gradual — beginners may add a pound or two of lean mass per month, less for experienced lifters.
Which lean body mass formula is most accurate?
The Boer formula is widely used and accurate for most adults; Hume and James are alternatives. All formulas are estimates — entering a measured body fat percentage gives the most reliable lean body mass figure.