Lean Body Mass Calculator
Lean body mass is everything that is not fat: muscle, bone, organs, water. It is the number that matters during a diet, because losing weight is easy and losing only fat is not. This calculator applies the Boer formula, which is widely used clinically and needs only height, weight and sex.
Inputs
Result
60.1 kg
Body fat mass ≈ 17.9 kg
How the lean body mass calculator works
Boer formula for men: LBM = 0.407 × weight in kg + 0.267 × height in cm − 19.2. For women: 0.252 × weight + 0.473 × height − 48.3.
Fat mass = total weight − lean body mass, and body fat percentage = fat mass ÷ weight × 100.
Lean mass also drives energy needs: it is the primary determinant of basal metabolic rate, which is why preserving it protects your maintenance calories.
Worked example: a woman, 165 cm, 68 kg
- 0.252 × 68 = 17.14.
- 0.473 × 165 = 78.05.
- LBM = 17.14 + 78.05 − 48.3 = 46.9 kg.
- Fat mass = 68 − 46.9 = 21.1 kg, about 31%.
- After losing 5 kg with resistance training and adequate protein, ideally lean mass stays near 46.9 and fat mass falls to 16 kg — roughly 25%.
Common mistakes to avoid
Assuming all weight loss is fat loss
In an aggressive deficit without resistance training, 25–30% of the loss can be lean tissue. That lowers your metabolic rate and makes regain easier.
Using a formula instead of tracking change
Boer estimates from height and weight only, so it cannot detect muscle you have built. Use it for a baseline and track measurements alongside it.
Under-eating protein while dieting
Below roughly 1.6 g per kg of bodyweight, lean mass retention suffers markedly during a deficit.
Frequently asked questions
What is lean body mass?
Total bodyweight minus fat mass — muscle, bone, organs, connective tissue and body water combined.
How do I preserve lean mass while dieting?
Keep the deficit moderate, eat 1.6–2.2 g of protein per kg of bodyweight, and lift weights two to four times a week.
Is lean body mass the same as muscle mass?
No. Skeletal muscle is roughly half of lean mass; the rest is bone, organs and water.
Why do drug doses use lean body mass?
Many drugs distribute through lean tissue rather than fat, so dosing on total weight can overdose people with high body fat.
How much muscle can I realistically gain?
Untrained people often gain 0.5–1 kg a month initially; after a few years it slows to a fraction of that per year.
Related calculators
Body Fat Calculator
Estimate body fat percentage with the US Navy method.
BMR Calculator
Basal metabolic rate using the Mifflin-St Jeor equation.
Protein Intake Calculator
Daily protein target based on weight and goal.
TDEE Calculator
Total daily energy expenditure from BMR and activity.
Ideal Weight Calculator
Devine formula ideal body weight from height.