Lean Body Mass (LBM) Calculator
Estimate your lean body mass — everything except stored fat, including muscle, bone, organs and water — from your height, weight and sex using the Boer formula. Lean mass is used to guide protein targets, some drug doses and body-composition goals. Enter your details in metric or imperial units.
The lean body mass formula
Boer (1984): men LBM = 0.407 × weight[kg] + 0.267 × height[cm] − 19.2; women LBM = 0.252 × weight[kg] + 0.473 × height[cm] − 48.3. Body-fat mass = total weight − LBM, and body-fat % = fat mass ÷ weight.
Frequently asked questions
How is lean body mass calculated?
Lean body mass here is calculated with the Boer formula. For men, LBM (kg) = 0.407 × weight(kg) + 0.267 × height(cm) − 19.2. For women, LBM = 0.252 × weight(kg) + 0.473 × height(cm) − 48.3. For an 80 kg, 180 cm man that is about 61.4 kg of lean mass, leaving roughly 18.6 kg (23%) as fat. Body-fat mass is simply total weight minus lean mass.
What is a normal lean body mass percentage?
Lean mass typically makes up about 70–90% of body weight, the mirror image of body fat. Because healthy body-fat ranges differ by sex (roughly 10–20% for men and 18–28% for women), so does lean-mass percentage. The absolute figure matters more than the percentage when tracking muscle over time.
Why does lean body mass matter?
Many things scale with lean mass rather than total weight: resting metabolic rate, protein requirements, and the dosing of certain drugs (especially anaesthetic and water-soluble agents). Preserving lean mass during weight loss is also a common fitness goal, since it keeps metabolism and strength up. Because lean mass is what remains after fat is subtracted, tracking it alongside total weight tells you whether a change on the scales came from fat or from muscle — something the weight alone cannot show. For an 80 kg man with 61.4 kg of lean mass, losing 3 kg of body weight is a very different result depending on whether lean mass stayed at 61 kg or fell with it.
Which lean body mass formula is this?
The Boer formula (1984), one of the most widely used equations for estimating lean mass from height and weight. Others include the Hume and James formulas; they give broadly similar numbers. All are population estimates and are least accurate at the extremes of body size or for very muscular people.
Is lean body mass the same as fat-free mass?
Lean body mass and fat-free mass are almost the same. Strictly, fat-free mass excludes all fat, while lean body mass includes the small amount of essential fat within organs and cell membranes, so LBM is marginally higher. In everyday use the two terms are treated as interchangeable, and this estimate covers both purposes.
This is a reference tool, not a diagnosis or medical advice. Results depend on the laboratory, assay and clinical context, and reference intervals vary between labs and by age and sex — always read your result against the range printed on your own report and discuss it with a qualified healthcare professional.
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