Calculate your lean body mass using 3 validated formulas (Boer, Hume, James). Compare results to understand your fat-free weight including muscle, bone, and organs.
Lean Body Mass (LBM) is everything in your body that isn't fat: muscle, bone, organs, water, and connective tissue. Knowing your LBM helps you understand your body composition beyond what a scale shows.
This calculator compares three validated estimation formulas — Boer (1984), Hume (1966), and James (1976) — which use height and weight to predict LBM without requiring body fat measurements. Each formula was derived from different populations, so comparing all three gives a more reliable estimate.
LBM is crucial for setting caloric needs (metabolism scales with lean mass, not total weight), medication dosing, and tracking fitness progress. Gaining muscle while losing fat can leave your scale weight unchanged while dramatically improving body composition. Whether you are a beginner or experienced professional, this free online tool provides instant, reliable results without manual computation. By automating the calculation, you save time and reduce the risk of costly errors in your planning and decision-making process.
Scale weight alone is misleading — it can't tell you whether changes come from muscle, fat, or water. LBM estimation gives a clearer picture of your body composition using only height and weight. It's particularly useful for tracking body recomposition during fitness programs where fat loss and muscle gain happen simultaneously.
Boer (1984): Men: LBM = 0.407 × W + 0.267 × H − 19.2 Women: LBM = 0.252 × W + 0.473 × H − 48.3 Hume (1966): Men: LBM = 0.32810 × W + 0.33929 × H − 29.5336 Women: LBM = 0.29569 × W + 0.41813 × H − 43.2933 James (1976): Men: LBM = 1.1 × W − 128 × (W/H)² Women: LBM = 1.07 × W − 148 × (W/H)² W = weight (kg), H = height (cm)
Result: Boer: 65.0 kg | Hume: 65.2 kg | James: 66.9 kg | Average: 65.7 kg | Est. BF: 19.9%
For a male at 178 cm and 82 kg: Boer = 0.407 × 82 + 0.267 × 178 − 19.2 = 65.0 kg. Hume = 0.32810 × 82 + 0.33929 × 178 − 29.5336 = 65.2 kg. James = 1.1 × 82 − 128 × (82/178)² = 66.9 kg. Average LBM ≈ 65.7 kg, implying ~16.3 kg fat mass (19.9% body fat).
Each formula was derived from a different research population. Boer (1984) used modern densitometry techniques and is considered the most broadly applicable. Hume (1966) was derived from radioactive potassium (40K) measurements in Scottish subjects. James (1976) used a non-linear equation that may better capture the relationship between weight and lean mass at extreme weights. No single formula is perfect for everyone — comparing all three provides a reality check.
Lean body mass is important in pharmacology. Many drug dosages (especially anesthetics, chemotherapy, and some antibiotics) are calculated based on LBM rather than total body weight, because fat tissue has different pharmacokinetic properties. This is why accurate LBM estimation matters in clinical settings, not just fitness.
Lean body mass includes everything that isn't fat: muscle, bone, organs, blood, water, and connective tissue. Skeletal muscle mass is only the voluntary muscles and typically makes up about 40-50% of total body weight in fit individuals. LBM is always higher than muscle mass. There's no simple formula to estimate muscle mass alone without advanced imaging like DEXA or MRI.
The Boer formula (1984) is generally considered the most accurate of the three for the widest range of body types, as it was validated against more modern measurement techniques. The James formula performs well for individuals of average build. Hume's formula tends to work best for taller individuals. Averaging all three reduces the impact of any single formula's bias.
Yes. LBM decreases with aging (sarcopenia loses ~3-8% of muscle mass per decade after 30), prolonged bed rest, severe caloric deficits, inadequate protein intake, or chronic illness. Resistance training and adequate protein (1.6-2.2 g/kg/day) are the primary strategies to maintain or increase LBM throughout life.
Your basal metabolic rate (BMR) is primarily determined by lean body mass, not total weight. Crash diets that cause LBM loss also reduce your metabolic rate, making future weight loss harder (the "metabolic adaptation" problem). Preserving LBM through adequate protein and resistance training during a caloric deficit keeps your metabolism higher and promotes fat-specific weight loss.
Water is part of lean body mass. Dehydration can reduce measured LBM by 1-3 kg, while water retention (from sodium, carbs, or menstrual cycle) can increase it by a similar amount. For consistent tracking, measure at the same time of day, under similar hydration conditions. Note that formula-based estimates like these are less affected by hydration than BIA (bioelectrical impedance) measurements.
LBM as a percentage of total weight varies: fit men typically have 75-85% LBM (15-25% body fat), fit women 70-80% LBM (20-30% body fat). Athletes may exceed 85% (men) or 80% (women). LBM below 70% for men or 65% for women generally indicates excess body fat. However, these are guidelines — optimal varies by age, sport, and individual factors.