Estimate your lean mass with the Boer, James and Hume formulas
Add it to get lean mass from weight × (1 − body fat).
Lean body mass · Boer formula
58.1 kg
Remaining (fat and other) mass: 16.9 kg
James formula
59.0 kg
Hume formula
54.4 kg
Formulas estimate from height and weight only; they are not a body scan.
More free tools: BMR and TDEE · Macros · Protein · Water · Calorie deficit
Lean body mass (LBM) is everything in your body that is not fat: muscle, bone, organs and water. If you know your body fat percentage, LBM = weight × (1 − body fat %). If not, estimate it from height and weight with the Boer, James or Hume formulas.
Weight (w) is in kilograms and height (h) in centimetres.
Boer, James and Hume are population equations. They do not know how muscular you are, so they can underestimate LBM for lean, muscular people and overestimate it for people with a lot of body fat. The body fat route is more direct but only as good as your body fat estimate.
Boer: 0.407 × 80 + 0.267 × 180 − 19.2 = 32.56 + 48.06 − 19.2 = 61.4 kg. James: 1.1 × 80 − 128 × (80 ÷ 180)² = 88 − 25.3 = 62.7 kg. Hume: 0.3281 × 80 + 0.33929 × 180 − 29.5336 = 57.8 kg.
From body fat: 80 × (1 − 0.18) = 65.6 kg. The height-weight formulas land at 58 to 63 kg, while the body fat route gives 65.6 kg. That gap is typical for a trained person.
Boer: 0.252 × 65 + 0.473 × 165 − 48.3 = 16.38 + 78.05 − 48.3 = 46.1 kg. James: 1.07 × 65 − 148 × (65 ÷ 165)² = 69.55 − 22.97 = 46.6 kg. Hume: 0.29569 × 65 + 0.41813 × 165 − 43.2933 = 44.9 kg.
From body fat: 65 × (1 − 0.28) = 46.8 kg. Here all four methods agree within about 2 kg.
Estimates, not medical measurements. For clinical decisions use DEXA or another assessment from a professional. This is general information for healthy adults, not medical advice. Talk to a doctor or registered dietitian if you are pregnant, under 18, have a medical condition or a history of disordered eating.
Lean body mass is your total weight minus fat mass. It includes muscle, bone, organs, connective tissue and water. It is the metabolically active part of your body.
Multiply your weight by (1 − body fat percentage ÷ 100). An 80 kg person at 18% body fat has 80 × 0.82 = 65.6 kg of lean body mass and 14.4 kg of fat.
For men, LBM = 0.407 × weight (kg) + 0.267 × height (cm) − 19.2. For women, LBM = 0.252 × weight + 0.473 × height − 48.3. It was published in 1984 for estimating lean mass from height and weight.
None is exact. Using your body fat percentage is the most direct, if the body fat figure is good. Among height-weight formulas, Boer and James are widely used and tend to agree closely for average builds.
No. Lean body mass includes muscle but also bone, organs and water. Skeletal muscle is only part of it, so your muscle mass is smaller than your lean mass.
There is no universal target because it scales with height and frame. Compare it to yourself over time, and look at lean mass as a share of weight, which is 100% minus body fat.
Yes. Gaining muscle while losing fat can leave scale weight unchanged while lean mass rises. This is why tracking body fat or measurements beats weight alone.