🏋️ Lean Body Mass Calculator
Your scale cannot tell muscle from fat, but lean body mass can: it is everything you weigh minus your fat. Lifters watch it to confirm they are gaining muscle, and dieters watch it to confirm they are losing fat rather than muscle.
Take your body fat percentage from the body fat calculator on this site, plug it in with your weight, and you get both numbers — lean mass and fat mass — in one glance.
How to use this calculator
Enter your weight and your body fat percentage, and the tool splits your weight into lean mass and fat mass.
- Enter your Weight in the kg field.
- Enter your Body fat percentage.
- Read the headline lean body mass figure.
- Check the fat mass row to see the other half of the split.
Frequently asked questions
What exactly is lean body mass?
Everything you weigh that is not fat: muscle, bone, water, organs and connective tissue. An 80 kg person at 20 percent body fat carries 64 kg of lean mass and 16 kg of fat mass.
Why track lean mass instead of weight?
The scale cannot tell muscle gain from fat gain. If your weight rises but your lean mass rises with it, you are building muscle; if your weight falls and lean mass holds steady, you are losing mostly fat.
Where do I get my body fat percentage?
Use the body fat calculator on this site for a tape-measure estimate, or a gym body-composition scale for a rough reading. Even an approximate figure makes the lean mass trend useful.
How often should I recheck?
Monthly is plenty. Lean mass changes slowly, so weekly readings mostly show water shifts. Compare readings taken under the same conditions, ideally in the morning.