Estimate your lean body mass (fat-free mass) based on weight, height, and gender.
Lean body mass is your total body weight minus fat mass - it includes muscle, bone, organs, and water. This calculator uses the Boer formula to estimate it.
Lean body mass - everything in the body that isn't fat, including muscle, bone, organs, and water - is a more useful number than total weight for certain purposes, particularly for tracking whether weight loss is coming from fat or from muscle, and for medical dosing calculations, where some medications are dosed based on lean mass rather than total body weight since fat tissue doesn't metabolize drugs the same way muscle and organ tissue do. Athletes and bodybuilders track lean body mass specifically because the goal during a cutting phase is to lose fat while preserving as much lean mass as possible, and total weight alone can't distinguish between the two.
Since lean body mass isn't directly measurable without specialized equipment like a DEXA scan or bioelectrical impedance device, most everyday calculators estimate it using formulas developed from population data (like the Boer or James formulas), based on height, weight, and sex - these give a reasonable estimate but aren't as precise as a direct clinical measurement.
These terms are sometimes used interchangeably, though technically lean body mass includes a small amount of essential fat (found in organs and cell membranes) while fat-free mass excludes all fat entirely - for most everyday and fitness purposes, the practical difference between the two is small enough not to matter.
Lean body mass refers to total body weight minus fat mass, encompassing muscle, bone, organs, and water content, and is typically estimated using formulas that factor in total weight, height, and sex, since these formulas were derived from population-level data correlating these measurements with directly measured lean mass. Lean body mass is often considered a more actionable metric than total body weight for fitness purposes, since the goal of many training and nutrition programs is specifically to preserve or increase lean mass while managing fat mass, rather than simply moving total weight in either direction.
Protein needs, calorie requirements, and even certain medication dosages are sometimes calculated based on lean body mass rather than total body weight, since lean tissue is metabolically active in ways that fat tissue generally isn't, making lean-mass-based calculations more physiologically accurate for these specific purposes than a simple total-weight-based estimate.
Because lean body mass estimation formulas rely on general population data rather than individual direct measurement, tracking the trend over time — rather than treating any single calculated number as precisely accurate — provides more useful information for monitoring whether a training and nutrition program is successfully preserving or building lean mass, particularly during a fat loss phase where losing some lean mass alongside fat is common but ideally should be minimized.
Lean tissue burns more calories at rest than fat tissue does, which means two people of identical total body weight but different lean mass proportions can have meaningfully different daily calorie needs. This is part of why building or preserving muscle mass through resistance training can modestly raise resting metabolic rate over time, beyond the calories burned during the workouts themselves.
It helps track fitness progress, calculate calorie and protein needs more precisely, and understand body composition beyond simple weight.
They give a reasonable estimate based on population data, but a direct clinical measurement like a DEXA scan is more precise for anyone who needs exact figures.
No, lean body mass includes muscle, bone, organs, and water - it's a broader category than muscle mass alone.
Fat tissue doesn't metabolize certain drugs the same way lean tissue does, so dosing based on lean mass can give a more accurate and safer dosage for some medications.
