Estimate how much of your weight is lean tissue. This free lean body mass calculator uses the Boer and James formulas to show your lean mass, fat mass and approximate body fat percentage.
Your details
cm
kg
ftin
lb
Lean body mass (Boer)
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Enter your height and weight
Fat mass (approx)
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Body fat % (approx)
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James formula
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Lean %
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An estimate from height, weight and sex — formulas can’t see your actual body composition. For precise measurement, methods like DEXA and professional guidance are best.
Use this free lean body mass calculator to estimate how much of your weight is lean (fat-free) tissue. Enter your height, weight and sex to see your lean body mass, fat mass and approximate body fat percentage.
What this lean body mass calculator shows you
A lean body mass (LBM) calculator estimates the weight of everything in your body that isn’t fat — muscle, bone, organs and water. Using your height, weight and sex, it shows your lean body mass, estimated fat mass and approximate body fat percentage, with a second formula as a cross-check.
For a man of 75 kg and 178 cm, the Boer formula gives about 59 kg of lean mass — roughly 78% of body weight, leaving around 16 kg (about 21%) as fat. The calculator also shows the James formula, which gives a similar figure as a sanity check.
How to use the lean body mass calculator
Select your sex and units.
Enter your height and weight.
Read your result. Lean mass, fat mass and body fat % appear instantly.
Why lean body mass matters
Medication dosing sometimes uses lean mass rather than total weight.
Fitness tracking — changes in lean mass help interpret training progress.
Nutrition planning — protein needs are often linked to lean mass.
Context for weight — two people of the same weight can have very different lean mass.
Lean body mass terms glossary
Term
What it means
Lean body mass
Body weight minus fat mass.
Fat mass
The weight of body fat.
Body fat %
Fat mass as a share of total weight.
Boer / James
Common formulas that estimate LBM from height and weight.
Lean Body Mass FAQ
What is lean body mass?
Lean body mass is your total weight minus body fat — it includes muscle, bone, organs and water. It's often used in fitness tracking, nutrition and certain medication dosing.
How is lean body mass calculated?
This calculator uses the Boer formula: for men, 0.407 × weight(kg) + 0.267 × height(cm) − 19.2; for women, 0.252 × weight + 0.473 × height − 48.3. It also shows the James formula as a cross-check.
What's the difference between lean mass and muscle?
They aren't the same. Lean body mass includes muscle plus bone, organs and water, so it's larger than muscle mass alone. Most simple calculators estimate lean mass, not muscle specifically.
How accurate are these estimates?
Formula-based estimates use only height, weight and sex, so they can't see your actual composition. Methods like DEXA scans, hydrostatic weighing or BIA are far more accurate.
Why does sex change the result?
On average, men and women differ in body composition, so the formulas use different constants for each to give a more realistic estimate.
Is the lean body mass calculator free to use?
Yes, this lean body mass calculator is completely free, needs no sign-up, and gives instant results directly in your browser.
