Lean Body Mass Calculator
Estimate how much of your weight is lean tissue.
Your result
Enter your details and press calculate to see your result.
Your data is never uploaded. All calculations happen in your browser.
Lean body mass (LBM) is everything in your body that is not fat: muscle, bone, organs, connective tissue and the water they hold. It is sometimes called fat-free mass, and together with your fat mass it adds up to your total body weight. Lean mass is what drives your strength and most of your resting metabolism, so knowing it tells you more about your physique than the scale alone. This calculator estimates your lean body mass and fat mass from just your sex, weight and height, without needing a body-fat measurement.
How lean body mass is calculated
We use the Boer formula, a height-and-weight equation published by P. Boer in 1984 and widely used in clinical and sports settings. It has separate versions for men and women because average body composition differs by sex. For men, LBM equals 0.407 times weight in kilograms plus 0.267 times height in centimetres minus 19.2. For women, LBM equals 0.252 times weight plus 0.473 times height minus 48.3.
Take a man weighing 80 kg at 178 cm. His lean body mass is 0.407 x 80 + 0.267 x 178 - 19.2, which equals 32.6 + 47.5 - 19.2, or about 60.9 kg. Subtracting that from his 80 kg total leaves roughly 19.1 kg of fat mass, near 24% body fat. The calculator does this split for you and shows both numbers.
Why lean mass matters
Lean tissue is metabolically active, so people with more of it burn more calories at rest. It also reflects your training: when you build muscle your lean mass rises, and when you lose muscle through inactivity or aggressive dieting it falls. Tracking lean mass alongside total weight tells you whether the weight you gain or lose is muscle or fat, which the scale on its own cannot.
During a calorie deficit the goal is to lose fat while keeping lean mass. Eating enough protein, around 1.8 to 2.2 grams per kilogram of body weight, and continuing to strength train both help preserve lean tissue so that most of the weight you drop comes from fat.
How accurate is this estimate
The Boer formula gives a solid estimate for people in a typical range of body composition, but it works from height and weight alone, so it cannot see how muscular or lean you actually are. A very muscular athlete and an untrained person of the same height and weight get the same result, even though their real lean mass differs. For a more precise figure, pair this estimate with a measured body-fat percentage from calipers, a DEXA scan or a bioelectrical impedance scale, then recalculate lean mass directly as weight times one minus your body-fat fraction.
How to use
- 01
Choose your sex
The Boer formula differs for men and women.
- 02
Enter weight and height
Add your measurements in metric or imperial.
- 03
See lean & fat mass
The result splits your weight into lean tissue and fat.
Frequently Asked Questions
Lean body mass is everything in your body that is not fat — muscle, bone, organs and water.
It drives your metabolism and strength. Preserving lean mass while dieting keeps your metabolism higher.
It is a solid estimate from height and weight. For precise numbers, combine it with a body-fat measurement.
Eat enough protein (1.8–2.2 g/kg) and keep strength training during a calorie deficit.
Related Calculators
Last reviewed June 2026 · Methodology & sources