Calculate your lean body mass using 3 established 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 body composition beyond what a scale shows.
This calculator compares three established 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 you a practical range rather than a single definitive value.
LBM is often used when estimating calorie needs, giving medication-dosing context, and tracking body-composition changes over time. Gaining muscle while losing fat can leave scale weight relatively unchanged even when body composition shifts.
Scale weight alone cannot tell you whether changes come from muscle, fat, or water. LBM estimation adds context using only height and weight, which can be useful when you want a rough body-composition reference without direct body-fat testing.
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 densitometry-based work, Hume (1966) drew from radioactive potassium (40K) measurements, and James (1976) used a non-linear equation that may behave differently at more extreme body sizes. No single formula is perfect for everyone, which is why showing all three results is more useful than presenting one as universally best.
Lean body mass can matter in pharmacology because some drugs are dosed from lean or adjusted body-size estimates rather than total body weight. This calculator does not replace formal dosing references, but it does show why LBM can matter in clinical as well as fitness contexts.
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This page applies three published lean-body-mass equations to the same height-and-weight inputs and shows the individual results plus an average. The formulas are treated as population-derived estimates, not direct measurements, so the result should be read as a practical reference range rather than a definitive body-composition value.
The optional body-fat-derived estimate is included only as a comparison aid when body-fat percentage is available. Where the formulas diverge, the calculator highlights that spread so users can judge how sensitive the estimate is to the chosen model.
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, Hume, and James formulas were developed from different populations, so none is a perfect fit for everyone. Many people use the three results as a practical range, then compare them with direct body-fat measurements or other body-composition data when available.
Yes. LBM can decrease with aging, prolonged bed rest, severe caloric deficits, inadequate protein intake, or chronic illness. Resistance training and sufficient protein intake are common strategies people use to help maintain it over time.
Lean body mass influences basal metabolic rate more than total weight alone. During weight loss, people often monitor LBM so they can watch for large drops that may reflect muscle loss rather than fat 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.