Lean Body Mass Calculator
Estimate your lean mass with 3 validated formulas
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Lean Body Mass Calculator
Lean body mass (LBM) is everything in your body except fat — muscle, bone, organs and water. This calculator estimates LBM from your weight, height and sex using three validated equations (Boer, James and Hume) and shows their average plus the resulting fat mass and body-fat percentage. Knowing LBM helps set realistic protein and calorie targets while you lose fat without losing muscle.
How to use this lean body mass calculator
Pick your gender, type in your weight and height, and use the toggle to switch between metric and imperial if you prefer pounds and inches. Press calculate and your lean body mass appears at once in kilograms — shown as an average alongside the Boer, James and Hume estimates, plus your fat mass and body-fat percentage. Nothing is stored and no sign-up is required, so you can rerun it as your numbers change.
How to read your result
Lean body mass is the non-fat part of you — muscle, bone, organs and water — so the figure represents everything except stored fat. At the same body weight, a higher LBM means you carry more muscle and less fat, a leaner build. The most useful move is to track it over time: during a fat-loss phase you want total weight to fall while LBM holds steady, which signals you are shedding fat rather than hard-won muscle.
The science behind the numbers
At its core, lean body mass is simply your weight minus your fat mass. When body fat is known, that subtraction is exact; when it is not, the tool estimates LBM from weight, height and sex. The Boer formula is a common example: for men, 0.407 times kg plus 0.267 times cm minus 19.2; for women, 0.252 times kg plus 0.473 times cm minus 48.3. LBM matters because both your protein needs and your BMR scale with lean tissue, not total weight.
Limits and practical tips
Formula estimates are convenient but they are not measurements: a DEXA or BIA scan can differ by a few kilograms, and the equations drift for edge cases such as very lean or obese bodies and unusually tall, short or heavily muscled athletes. For the sharpest result, feed in a measured body-fat percentage. For a fuller picture, pair this with CaloNote's Body Fat, FFMI, Protein and BMR calculators, and log your weight and meals in the CaloNote app to watch lean mass trend over weeks.
Frequently Asked Questions
- What is lean body mass?
- Lean body mass (LBM) is your total body weight minus fat mass, including muscle, bone, organs, and water. This calculator estimates it from your weight, height, and sex, and also reports your fat mass.
- Which lean body mass formula should I use?
- CaloNote shows the Boer, James, and Hume estimates so you can compare. The Boer formula is widely used and generally accurate for adults, while viewing all three gives a sensible range rather than relying on one equation.
- Why does lean body mass matter?
- LBM drives your resting metabolic rate and reflects how much muscle you carry, so tracking it helps ensure weight loss comes from fat rather than muscle. It is also used to set protein needs and calorie targets more precisely than weight alone.