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Estimate lean body mass and fat mass in kg using the averaged Boer, Hume and James formulas for men and women — useful for BMR, dosing and physique tracking.
Health
Generated on May 23, 2026
Estimate lean body mass and fat mass in kg using the averaged Boer, Hume and James formulas for men and women — useful for BMR, dosing and physique tracking.
Lean Body Mass (LBM) is your total body weight minus body fat — the weight of your muscles, bones, organs, connective tissue, and water. It is a far more meaningful metric than total scale weight for many purposes: medication dosing (some drugs are dosed by LBM rather than total weight for accuracy), metabolism estimates (LBM drives BMR), and muscle-building program design (gaining LBM while holding fat steady is the ideal result). This calculator uses three validated formulas (Boer, Hume, and James) and averages them to reduce individual formula bias.
Formula
Boer (male): LBM = 0.407 × Weight + 0.267 × Height − 19.2. Boer (female): LBM = 0.252 × Weight + 0.473 × Height − 48.3. (Weight in kg, Height in cm)Scale weight tells you very little useful. Lean Body Mass — your weight minus fat — tells you almost everything that actually matters. It's the weight of your muscles, bones, organs, connective tissue, and body water, and it's what drives your metabolism, your medication dosing accuracy, and the realistic ceiling of how strong you can get. Two adults at 80 kilos can be wildly different: one with 65 kg LBM and 15 kg fat is in athletic shape; one with 50 kg LBM and 30 kg fat is metabolically struggling despite weighing the same. This calculator averages three published formulas (Boer, Hume, James) instead of relying on one — averaging reduces individual formula bias and lands within roughly 5 percent of a DEXA scan, which is good enough for tracking real progress at home. The big insight most people miss: after 30, you lose 3 to 8 percent of muscle per decade unless you actively defend it with strength training and adequate protein. This is called sarcopenia and it's why your father gets weaker every year while looking the same on the scale — fat is quietly replacing muscle. Building LBM is a slow game: natural gains for beginners run 0.25 to 0.5 kg of muscle per month with proper training and protein, and slower for the experienced. Consistency over years is what compounds. Pro tip: track LBM monthly, not weekly, and combine with tape measurements and photos in consistent lighting for a real picture.
Lean Body Mass (LBM) is your total body weight minus body fat — the weight of your muscles, bones, organs, connective tissue, and water. It is a far more meaningful metric than total scale weight for many purposes: medication dosing (some drugs are dosed by LBM rather than total weight for accuracy), metabolism estimates (LBM drives BMR), and muscle-building program design (gaining LBM while holding fat steady is the ideal result). This calculator uses three validated formulas (Boer, Hume, and James) and averages them to reduce individual formula bias.
These empirically derived formulas predict lean body mass from weight and height, with distinct equations for men and women because women naturally carry more essential fat for hormonal and reproductive health. The calculator averages three published formulas (Boer, Hume, James) because each has slightly different assumptions and population bases — averaging reduces the noise and gives a more reliable estimate than any single formula alone. The difference between total weight and LBM is an estimate of your body fat mass.
Typical lean body mass for common adult body profiles. Values derived from averaged Boer/Hume/James formulas.
| Profile | Weight (kg) | Height (cm) | LBM (kg) | Fat Mass (kg) |
|---|---|---|---|---|
| Male | 60 | 170 | 52 | 8 |
| Male | 70 | 175 | 58 | 12 |
| Male | 80 | 180 | 63 | 17 |
| Male | 90 | 185 | 68 | 22 |
| Male | 100 | 185 | 71 | 29 |
| Female | 50 | 160 | 40 | 10 |
| Female | 60 | 165 | 45 | 15 |
| Female | 70 | 170 | 49 | 21 |
| Female | 80 | 175 | 53 | 27 |
| Female | 90 | 175 | 55 | 35 |
Women typically have 10–15% less lean body mass than men at the same height and weight.
Adults lose 3–8% of muscle per decade after age 30 (sarcopenia) — strength training reverses this.
LBM only ~50% is skeletal muscle — the rest is bone, organs, connective tissue, and water.
Natural muscle gain for beginners: 0.25–0.5 kg/month with proper training and protein; much slower for advanced lifters.
A male at 80 kg and 180 cm has approximately 61.5 kg LBM and 18.5 kg body fat (about 23% body fat).
A female at 60 kg and 165 cm has roughly 45 kg LBM and 15 kg body fat (about 25% body fat).
A male athlete at 90 kg and 185 cm has around 71 kg LBM and 19 kg body fat (roughly 21%).
A female at 55 kg and 160 cm has approximately 42 kg LBM and 13 kg body fat (about 24%).
Comparing two 75 kg men: one at 165 cm and one at 185 cm — the taller one has roughly 4 kg more LBM, which explains why taller men often look leaner at the same weight.
A 70-year-old at 70 kg might have 8 kg less LBM than a 30-year-old at the same weight due to age-related muscle loss (sarcopenia) — one reason why strength training becomes more important with age.
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