Estimate adult lean body mass with the Boer, James, and Hume equations, or calculate it directly when body fat percentage is known.
Lean body mass is body weight minus fat mass. It includes skeletal muscle, but also bone, organs, body water, blood, and connective tissue. It must not be interpreted as skeletal muscle mass alone.
In common calculator usage, lean body mass and fat-free mass are often treated similarly, although body-composition terminology can differ between measurement models. Formula estimates are predictions from height, weight, and sex rather than direct measurements.
W is kilograms and H is centimeters. Boer developed the equation while evaluating lean body mass as an index for body-fluid volumes.
Male: 0.407W + 0.267H − 19.2 · Female: 0.252W + 0.473H − 48.3W is kilograms and H is centimeters. Its squared weight-to-height term can behave differently at body-size extremes.
Male: 1.10W − 128(W²/H²) · Female: 1.07W − 148(W²/H²)W is kilograms and H is centimeters. Hume derived height-and-weight regression equations for predicting lean body mass.
Male: 0.32810W + 0.33929H − 29.5336 · Female: 0.29569W + 0.41813H − 43.2933This is direct arithmetic from the supplied body-fat percentage. Its accuracy depends on the accuracy and definition of that percentage.
Lean mass = weight × (1 − body fat % ÷ 100) · Fat mass = weight − lean massMale, 180 cm, 80 kg: Boer estimates 61.42 kg, James 62.716… kg, and Hume 57.7866 kg. Their average is 60.6408… kg, displayed as 60.6 kg.
Direct example: at 80 kg and 20% body fat, lean body mass is 80 × (1 − 0.20) = 64 kg, and fat mass is 16 kg.
Differences are expected because the equations use different coefficients and source populations. No method is marked as universally best.
Height, weight, hydration, clothing, and body-fat measurement error can affect comparisons over time.
Lean body mass includes water, organs, bone, connective tissue, and other non-fat components in addition to muscle.
Skeletal muscle is only one part of lean body mass. An LBM estimate cannot tell how much of the result is skeletal muscle, organ tissue, bone, or water.
The terms are frequently used interchangeably in prediction equations, but body-composition models may distinguish lean soft tissue, fat-free mass, and lean body mass. Always compare values produced with the same method and definition.
Boer and Hume use linear combinations of height and weight. James uses a nonlinear weight-squared-to-height-squared term. These mathematical and population differences produce different results, particularly at body-size extremes.
Regression formulas cannot identify an individual's actual tissue composition. Hydration, unusual muscularity, edema, measurement error, and differences from the original study populations can change how representative an estimate is. The direct method inherits the limitations of the body-fat measurement supplied.
It is body weight excluding fat mass, including muscle, bone, organs, water, blood, and connective tissue.
No. Skeletal muscle is only one component of lean body mass.
It can be predicted from height, weight, and sex with equations, or calculated arithmetically from weight and a known body-fat percentage.
No equation is universally most accurate. Performance varies by person, population, body size, and intended use.
They are often used similarly, but terminology can vary across body-composition models and measurement systems.
Yes. Multiply weight by one minus the body-fat fraction. The result is only as reliable as the supplied body-fat estimate.
They were derived using different equations, coefficients, and source data.
Body water is part of lean mass, so hydration affects measured body composition and can influence comparisons.
They can view the estimates, but unusual muscularity may make population equations less representative.
No. It is intended for adults and does not use pediatric body-composition methods.
Original and clinical formula references.