Body Composition: Looking Beyond the Scale
Why the number on the scale tells only part of the story — body fat, lean mass, the FFMI, where fat is stored, and how to measure and track your true body composition.
Lean Body Mass Calculator
Verified formula Updated Jun 2026 Private — runs on your device
Verified formula
Private
Lean body mass
56.00
- Fat mass
- 14.00
For general information only — not financial, tax, legal or medical advice. Verify before you rely on it.
How to use the Lean Body Mass Calculator
The Lean Body Mass Calculator works out your lean body mass, along with 1 related figure in an instant. Enter body weight and body fat percentage and the result updates as you type — it is free, needs no sign-up, and runs entirely in your browser so your figures stay private.
- Enter the body weight.
- Enter the body fat percentage.
- Read off your lean body mass, together with fat mass — the calculator updates automatically, with no button to press.
Formula
The Lean Body Mass Calculator uses the formula:
Lean body mass = Body weight × (1 - Body fat percentage ÷ 100)
Worked example
For example, with body weight of 70 kg and body fat percentage of 2%, the lean body mass is 56.00.
| Body weight | 70 kg |
|---|---|
| Body fat percentage | 2% |
| Lean body mass | 56.00 |
|---|---|
| Fat mass | 14.00 |
Results are estimates for educational use, not professional advice.
Key terms explained
- Percentage
- A number expressed as a fraction of 100, written with the % sign.
- Body fat
- The proportion of your body weight that is fat, as opposed to muscle, bone and water.
- Lean body mass
- Your total weight minus fat — muscle, bone, organs and water.
Frequently asked questions
Lean body mass is your total weight minus fat — it includes muscle, bone, organs and water. For a 70 kg person at 20% body fat, lean mass is 70 × 0.80 = 56 kg.
The calculator multiplies your weight by one minus your body fat fraction. You need a body fat percentage, which you can estimate from a body fat calculator or a body composition scan.
It is used to set protein needs, calorie targets and medication doses, and to track whether weight changes are fat or muscle.
It is only as accurate as your body fat percentage. Methods like calipers, bioimpedance scales and DEXA scans vary, so treat the result as an estimate.
Enter the body weight. Enter the body fat percentage. Read off your lean body mass, together with fat mass — the calculator updates automatically, with no button to press.
Related guides
Lean Body Mass Table: Lean body mass by Body weight
Reference table of lean body mass for Lean Body Mass across a range of body weight values — exact, engine-computed figures you can read off at a glance.
How to Calculate Lean Body Mass: Formula, Steps & Examples
Learn how to calculate Lean Body Mass — the formula explained step by step, with worked examples and a free calculator to check your answer.