Lean Body Mass Calculator
Estimate your lean body mass and body fat percentage with the Boer formula.
How to use
- Enter your weight and height in your preferred units.
- Click Calculate.
- See your lean body mass and estimated body fat %.
For information only — not medical advice. Consult a healthcare professional for personal guidance.
What Is a Lean Body Mass Calculator?
Lean body mass (LBM) is everything in your body that is not fat: muscle, bone, organs, water, and connective tissue. It is arguably the most important number in physique and performance nutrition, because your lean mass — not your total weight — drives your metabolism, your protein requirements, and how you will look when fat comes off. This calculator estimates your LBM from your gender, weight, and height using the Boer formula.
The distinction matters most during weight loss. Two dieters can each lose 10 kg, but if one loses 9 kg of fat and 1 kg of lean tissue while the other loses 6 kg of fat and 4 kg of lean tissue, their results — in strength, shape, and metabolic rate — are completely different. Tracking lean mass is how you tell the difference, and protecting it with protein and resistance training is the central skill of good dieting.
How to Use the Lean Body Mass Calculator
- Select your gender — the formula's coefficients differ for men and women.
- Enter your body weight in kilograms or pounds.
- Enter your height in centimeters, or in feet and inches.
- Click Calculate to see your estimated lean body mass (and the implied fat mass).
The Boer Formula
Published by P. Boer in 1984 from body-composition measurements, the formula estimates LBM directly from weight (W, kg) and height (H, cm). For men: LBM = (0.407 × W) + (0.267 × H) − 19.2. For women: LBM = (0.252 × W) + (0.473 × H) − 48.3. Height-based formulas like Boer's correlate well with measured lean mass in general populations because taller people carry more bone, organ, and muscle tissue at any given weight. Subtracting LBM from total weight gives fat mass, and dividing gives an implied body fat percentage.
What to Do With Your LBM Number
- Set protein from it: a common evidence-based target during dieting or muscle gain is roughly 2.0–2.2 g of protein per kilogram of lean mass per day.
- Estimate calories with it: formulas that use LBM (such as Katch-McArdle) outperform weight-only formulas when body composition is known.
- Track it quarterly during a diet: stable LBM with falling weight means the plan is working exactly as intended.
How accurate is the Boer formula?
For typical adults it agrees with DEXA-measured lean mass within a few kilograms. It assumes an average relationship between height, weight, and composition, so it is less precise for competitive bodybuilders, people with obesity, and the very elderly. For tracking change over time — its main job — the consistency of the method matters more than absolute precision.
Is lean body mass the same as muscle mass?
No — muscle is only part of it. Lean body mass also includes bone, organs, skin, blood, and body water (which alone is over half of LBM). Skeletal muscle is typically around 40–50% of lean mass in men and somewhat less in women. This is why LBM can swing a kilogram or two with hydration and glycogen while actual muscle changes slowly.
Can I increase lean body mass while losing fat?
Yes, under the right conditions: beginners, people returning after a layoff, and those with higher body fat can gain muscle in a modest calorie deficit when protein is high and training is progressive. Experienced lean lifters usually cannot, and do better alternating dedicated gaining and losing phases. Either way, LBM tracking tells you which side of the trade you are on.
Why do women use a different formula?
At the same height and weight, women on average carry more essential fat and less lean tissue than men — a hormonal and reproductive difference, not a fitness judgment. Separate coefficients keep the estimate unbiased for both sexes. The gap narrows but never disappears even among trained athletes, which is why all classic body-composition formulas are sex-specific.