Lean Body Mass Calculator
Estimate lean body mass and body fat from height and weight.
Formula
About this calculator
Lean body mass (LBM) is everything in your body that is not stored fat — muscle, bone, organs, connective tissue and water. Tracking it is often more useful than watching scale weight alone, because it tells you whether changes come from muscle or fat. This calculator estimates your LBM, and by extension your body-fat percentage, from just your height, weight and sex.
It uses the Boer formula as its primary estimate, the equation most widely cited in clinical and research settings, and shows the Hume formula alongside it as a cross-check. Both combine your weight and height with sex-specific constants; men carry more lean mass than women at the same size, which the different coefficients reflect. Subtracting lean mass from total weight gives an estimated fat mass and body-fat percentage.
Knowing your lean mass has practical uses. Protein targets are often set per kilogram of lean mass rather than total weight, resting metabolic rate scales with it, and during a diet the goal is to lose fat while preserving LBM. Watching this number instead of scale weight helps you tell a successful body-recomposition from simple weight loss.
These are population-based estimates from height and weight, not direct measurements. Methods like DEXA scans, hydrostatic weighing or skinfold calipers measure body composition more precisely. Use this calculator to spot trends over time rather than treating any single figure as exact.
Frequently asked questions
What is lean body mass?
Everything in your body except stored fat — muscle, bone, organs and water. It typically makes up most of your body weight.
Which formula is more accurate?
The Boer formula is the most widely used clinical estimate and is shown as the primary result; the Hume value is provided as a cross-check. Both are estimates from height and weight.
Why track lean mass instead of weight?
It reveals whether changes are muscle or fat. During a diet you want to keep lean mass while losing fat, something scale weight alone can't tell you.
How can I measure it more precisely?
DEXA scans, hydrostatic weighing and skinfold calipers give more accurate body-composition readings than any height-and-weight formula.
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⚠️ Lean-mass estimates are general guidance, not medical advice, and are less precise than DEXA or hydrostatic measurement. Consult a professional for clinical assessment.