Lean Body Mass
Lean mass is what remains after subtracting fat. If it holds steady while you lose weight, you lost fat and not muscle.
Your numbers
Lean mass
56kg
Fat mass
14kg
Formula
Lean mass = Weight (kg) × (1 − Body fat ÷ 100)
Cutting weight without protein and resistance training takes lean mass down with the fat.
What to enter
| Input | Default | Accepted range |
|---|---|---|
| Weight (kg)The second weight you are comparing against. | 70 | 10 ~ 300 |
| Body fat (%)The share of body weight that is fat. | 20 | 1 ~ 70 |
Step by step
Quick reference table
Results when only Weight (kg) changes and everything else stays put.
| Weight (kg) | Lean mass (kg) | Fat mass (kg) |
|---|---|---|
| 35 | 28 | 7 |
| 52.5 | 42 | 10.5 |
| 70 | 56 | 14 |
| 105 | 84 | 21 |
| 140 | 112 | 28 |
What each result means
| Result | At default values |
|---|---|
| Lean mass (kg)Everything that is not fat — muscle, bone, water. | 56 |
| Fat mass (kg)How much of your weight is fat, in kilograms. | 14 |
Common mistakes
Cutting weight without protein and resistance training takes lean mass down with the fat.
Glossary
- Weight (kg)
- The second weight you are comparing against.
- Body fat
- The share of body weight that is fat.
- Lean mass
- Everything that is not fat — muscle, bone, water.
- Fat mass
- How much of your weight is fat, in kilograms.
Frequently asked questions
Q. How is Lean Body Mass calculated?
Lean mass = Weight (kg) × (1 − Body fat ÷ 100) — Lean mass is what remains after subtracting fat. If it holds steady while you lose weight, you lost fat and not muscle.
Q. Can you walk through an example?
With Weight (kg) 70, Body fat 20%, the answer is Lean mass 56kg.
Q. What do I need to enter?
Enter Weight (kg), Body fat. The result recalculates as you type, and an empty box counts as zero.
Q. How much does the answer move if I change a number?
Changing only Weight (kg) moves the answer to Weight (kg) 35 → Lean mass (kg) 28 and Weight (kg) 140 → Lean mass (kg) 112. The table below lays out five steps.
Q. How are the numbers rounded?
Money is shown to the nearest whole unit, percentages to one decimal place and everything else to two. What you see is rounded; the calculation itself carries the unrounded value forward.
Q. Anything to watch out for?
Cutting weight without protein and resistance training takes lean mass down with the fat.
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