Lean Body Mass Calculator
Estimate your lean body mass — everything except fat — from height, weight, and sex using the Boer formula. Useful for setting protein, calorie, and medication targets.
Last updated: May 2026
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About this calculator
Lean body mass (LBM) is the total weight of your body minus its fat — it includes muscle, bone, organs, connective tissue, and body water. This calculator uses the Boer formula, one of the most validated population equations: 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. The sex-specific coefficients reflect the fact that, on average, men carry more muscle and less fat than women at the same height and weight. LBM is a more useful basis than total body weight for several practical decisions: protein intake is often prescribed per kilogram of lean mass, resting metabolic rate scales with lean tissue, and the dosing of some medications and anesthetics is calculated from lean rather than total weight to avoid overdosing in people with high body fat. Edge cases and limits: the Boer formula is an estimate from body measurements, not a direct measurement, so it is less accurate for very muscular athletes, the very obese, the elderly, and children, whose body composition departs from population averages. It cannot match the precision of DEXA scans, hydrostatic weighing, or bioelectrical impedance. Because LBM and body-fat percentage are complementary (fat mass = total weight − LBM), this estimate also implies a rough body-fat figure, but for serious tracking a direct composition measurement is preferable.
How to use
Example 1 — an 80 kg, 180 cm man. Enter Weight = 80, Height = 180, Sex = Male. LBM = 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.42 kg. Verify: that implies about 18.6 kg of fat mass (80 − 61.42), or roughly 23% body fat — a plausible figure for an average adult man. Example 2 — a 65 kg, 165 cm woman. Enter Weight = 65, Height = 165, Sex = Female. LBM = 0.252 × 65 + 0.473 × 165 − 48.3 = 16.38 + 78.05 − 48.3 = 46.13 kg. Verify: fat mass is about 18.9 kg (65 − 46.13), or roughly 29% body fat, which is within the typical range for a healthy adult woman, who naturally carries more essential fat than a man.
Frequently asked questions
What is the difference between lean body mass and muscle mass?
They are related but not the same. Lean body mass is everything in your body that is not fat — it includes skeletal muscle but also bone, organs, skin, connective tissue, and the large amount of water your body holds. Muscle mass specifically refers to skeletal muscle, which is only a portion of total lean mass (often around half). People sometimes assume gaining lean mass means gaining only muscle, but changes in body water or glycogen can shift lean mass figures too. If your goal is muscle growth specifically, lean body mass is a useful proxy but not a direct measure. For precise muscle tracking, methods like DEXA that separate tissue types are needed.
How accurate is the Boer formula?
The Boer formula is one of the better-validated population equations and works well for average adults, but it is an estimate based only on height, weight, and sex — not a measurement of your actual tissue. It tends to be less accurate at the extremes: it can underestimate lean mass in very muscular athletes and overestimate it in people with very high body fat, because their composition differs from the population average it was derived from. It is also not validated for children or for some clinical populations. For everyday goal-setting it is perfectly serviceable, but if you need precision — for research, medical dosing, or detailed physique tracking — a DEXA scan, hydrostatic weighing, or bioelectrical impedance gives a direct reading. Treat the formula's output as a good ballpark, not a definitive number.
Why is lean body mass useful for nutrition and training?
Lean body mass is a better basis than total weight for several decisions because fat tissue is relatively metabolically inactive. Protein needs are often expressed per kilogram of lean mass (commonly 1.6–2.2 g/kg LBM for those building muscle), which avoids overestimating requirements in people carrying more fat. Resting metabolic rate also scales primarily with lean tissue, so LBM helps refine calorie targets. And tracking LBM during a diet helps confirm you are losing fat rather than muscle — the goal of most fat-loss programs. Using total body weight for these calculations can mislead, especially for people at the higher or lower ends of body fat. That is why coaches and clinicians often prefer lean-mass-based targets.
When should I NOT use this lean body mass estimate?
Avoid relying on it for very muscular athletes, the very obese, the elderly, pregnant women, or children, because their body composition departs from the population averages the Boer formula was built on, producing meaningful errors. Do not use it for clinical decisions such as drug dosing without professional oversight — clinicians use validated, context-specific methods. It should not replace a direct body-composition measurement when accuracy genuinely matters, such as research or detailed physique competition prep. And because it is sex-binary and based on average physiology, it may fit poorly for individuals whose body composition differs from the norm. Use it as a convenient estimate for general fitness and nutrition planning, and seek direct measurement when precision is important.
How do I find my body fat percentage from lean body mass?
It is a simple subtraction: your fat mass equals total body weight minus lean body mass, and your body-fat percentage is fat mass divided by total weight, times 100. For instance, an 80 kg man with 61.42 kg of lean mass has 18.58 kg of fat, or about 23.2% body fat. This is a handy by-product of the LBM estimate, but remember it inherits all the formula's limitations — it is only as accurate as the lean-mass estimate it is derived from. For a more reliable body-fat figure, use a method designed to measure it directly, such as skinfold calipers, the Navy tape method, bioelectrical impedance, or a DEXA scan. The subtraction approach is best for a quick estimate rather than precise tracking.