Free Tool · Body Composition
Lean Body Mass Calculator
Estimate your lean body mass and implied body-fat percentage using the Boer formula. Lean mass is the part of your weight that is not fat: muscle, bone, organs, water, glycogen. Tracking it tells you whether weight changes come from fat, muscle, or water.
How it works
The Boer formula
The Boer equation predicts lean body mass from biological sex, height, and weight. It was developed by P. Boer in 1984 and outperformed both the Hume and James formulas in subsequent comparisons against DEXA scans.
For men: LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2. For women: LBM = 0.252 × weight (kg) + 0.473 × height (cm) − 48.3.
Subtract LBM from your total weight to get fat mass. Divide fat mass by total weight to get body-fat percent. The calculator does both steps for you.
Reference ranges
Lean mass benchmarks
| Population | Typical lean mass % |
|---|---|
| Untrained adult man | 75 to 80% |
| Untrained adult woman | 68 to 75% |
| Recreational lifter (man) | 82 to 88% |
| Recreational lifter (woman) | 75 to 82% |
| Competitive bodybuilder (off-season) | 88 to 92% |
Frequently asked questions
Questions we hear a lot
Lean body mass (LBM), sometimes called fat-free mass, is everything in your body that is not fat: muscle, bone, organs, water, glycogen. Tracking LBM separately from total weight tells you whether the scale is moving because of fat, muscle, or water shifts.
The Boer equation has the smallest mean error against DEXA scans for adults across normal-to-overweight ranges in published comparisons. The Hume and James formulas tend to overestimate at higher body weights. Boer is the default for most clinical and athletic use cases when DEXA is not available.
Predictive equations like Boer estimate LBM within roughly 5 to 8 percent of a DEXA measurement for most adults. Highly muscular athletes and people with very high body fat sit at the edges of the formula's calibration data, so accuracy drops there. Use the output as a directional baseline.
They are two sides of the same equation. Total weight minus lean body mass equals fat mass. The fat mass divided by total weight is your body fat percent. The Boer formula here estimates LBM directly; the implied body-fat percent comes from subtracting LBM from your weight.
A common evidence-based target is 0.7 to 1.0 grams of protein per pound of LBM during a cut and 0.6 to 0.8 g/lb LBM at maintenance or surplus. Using LBM instead of total weight prevents you from over-eating protein when carrying significant body fat.
For most lifters and recreational athletes, an LBM calculator is enough to set training and nutrition targets. DEXA, BodPod, or hydrostatic weighing become worth the cost when you need precise tracking inside a small range, like preparing for a physique show or running a structured research-style program.