Lean Body Mass Calculator
Find your lean body mass using proven formulas — enter your stats below.
Leave at default if you don't know your body fat %.
| Formula | LBM | Fat Mass |
|---|
| Metric | Value |
|---|
How to Use This Lean Body Mass Calculator
Select your unit system (imperial or metric), enter your sex, weight, and height, then optionally slide your known body fat percentage. Choose a formula method or select "Show All Methods" to compare. Hit Calculate to instantly see your lean body mass, fat mass, and a breakdown by formula.
The body fat % slider enables the direct measurement method — if you've had a DEXA scan, hydrostatic weighing, or use a reliable body fat caliper, enter that value for the most accurate result.
Why This Matters
Lean body mass (LBM) is the weight of everything in your body except fat — muscles, organs, bones, water, and connective tissue. It's one of the most useful metrics in fitness and health because it tells you what you're actually working with.
For someone like a 180 lb man at 22% body fat, LBM works out to around 140 lbs. That number matters more than total weight for setting protein targets (most research recommends 0.7–1g of protein per pound of LBM), calculating accurate caloric needs, and tracking real progress during a cut or bulk. The scale can stay the same while you lose fat and gain muscle — only LBM tracking reveals that.
Athletes, personal trainers, and sports nutritionists use LBM to prescribe medication dosages (several drugs are dosed by LBM, not total weight), set strength benchmarks, and monitor the effectiveness of training programs. Even outside elite athletics, knowing your LBM helps you set realistic expectations: two people at the same BMI can have very different body compositions.
It's also valuable for tracking aging — adults lose 3–8% of muscle mass per decade after 30, and LBM monitoring catches this early, allowing intervention through resistance training and adequate protein intake.
How It's Calculated
Three established clinical formulas estimate LBM from height and weight alone. Each was derived from different population studies:
Male: LBM = (0.407 × W) + (0.267 × H) − 19.2
Female: LBM = (0.252 × W) + (0.473 × H) − 48.3
James (1976):
Male: LBM = 1.1W − 128(W/H)²
Female: LBM = 1.07W − 148(W/H)²
Hume (1966):
Male: LBM = (0.3281 × W) + (0.3393 × H) − 29.5336
Female: LBM = (0.2969 × W) + (0.4169 × H) − 43.2933
Direct (Body Fat %):
LBM = Total Weight × (1 − Body Fat% / 100)
Where W = weight in kg and H = height in cm. The direct body fat % method is the most accurate if you have a reliable measurement.
Tips & Common Mistakes
- Don't rely on a single formula. Average the Boer, James, and Hume results for a more reliable estimate if you don't know your body fat %.
- Use the direct method when possible. A DEXA scan or hydrostatic weighing is accurate to ±1–2%; scale-based impedance readings can vary ±5%.
- Weigh yourself consistently. Morning, post-bathroom, pre-food measurements eliminate daily fluctuations from food and water weight.
- LBM ≠ muscle mass. Lean body mass includes bones, organs, and water. Skeletal muscle is roughly 40–50% of LBM in healthy adults.
- Retest at the same conditions. Tracking changes over time requires consistency — same time of day, same hydration state, same scale.