Lean Body Mass Calculator
Calculate your Lean Body Mass using Boer, James, and Hume formulas. Shows average LBM, fat mass, and body fat percentage.
Average Lean Body Mass
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Fat Mass
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Est. Body Fat%
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LBM as % of Weight
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By formula
LBM estimates are derived from height and weight only. For greater accuracy, use a body fat measurement method such as the US Navy circumference method.
What is Lean Body Mass Calculator?
The Lean Body Mass (LBM) Calculator estimates the weight of everything in your body except fat — including muscle, bone, organs, connective tissue, and water. It uses three established formulas (Boer 1984, James 1976, and Hume 1966) and reports all three results plus their average, giving you a robust baseline for tracking muscle gain or loss. LBM is used in clinical nutrition, drug dosing, and BMR calculation — the Katch-McArdle BMR formula uses LBM directly and is more accurate than weight-based formulas for lean individuals.
How to use
- 1 Select your biological sex.
- 2 Enter your height in centimetres and your total body weight in kilograms.
- 3 Review your average lean body mass and estimated fat mass.
- 4 Check the breakdown by each individual formula for reference.
Formula
Example calculation
A 70 kg male, 175 cm: Boer = 57.3 kg, James = 57.1 kg, Hume = 56.9 kg. Average LBM = 57.1 kg. Fat mass = 70 − 57.1 = 12.9 kg (18.4% body fat).
Frequently asked questions
What is lean body mass used for?
LBM is used in clinical nutrition, drug dosing, fitness programming, and body composition tracking. The Katch-McArdle BMR formula uses LBM instead of total weight, making it more accurate for lean or athletic individuals. Drug dosing in critical care often references LBM to avoid overdosing obese patients.
How is LBM different from muscle mass?
Lean body mass includes all non-fat tissue: muscle, bone, organs, connective tissue, blood, and water. Skeletal muscle mass is just one component. LBM is always significantly larger than muscle mass alone — bone and organs make up a substantial portion.
Which formula is most accurate?
All three formulas were validated on different populations and each has its own error range. The Boer formula tends to perform well in general populations. The average of all three is generally a more robust estimate than any single formula alone, as it reduces the impact of any one formula's population-specific bias.
Can I use LBM to estimate body fat?
Yes. Fat mass = total weight − LBM. Body fat% = fat mass / total weight × 100. This gives a reasonable estimate but is less accurate than direct measurement methods like DEXA or hydrostatic weighing. For better accuracy, use the US Navy circumference method in the Body Fat Calculator.
Why does LBM matter when losing weight?
During weight loss through diet alone, some of the loss is muscle in addition to fat. Resistance training while in a calorie deficit helps preserve LBM. Tracking LBM alongside total weight gives a clearer picture of whether you are losing fat or muscle.