Using the Lean Body Mass Calculator
Enter weight in kilograms and body fat as a percentage, such as 20 rather than 0.20. At 70 kilograms and 20% body fat, estimated fat mass is 14 kilograms and lean mass is 56 kilograms. Together the two values add back to total body weight.
Worked example
Use the example inputs below to reproduce this result. These are the form's starting values, not recommended targets. Changing your inputs updates your result above; this worked example stays fixed for comparison. Results are rounded for display.
Example inputs
- Weight (kg)
- 70
- Body fat (%)
- 20
Example result
- Lean body mass (kg)
- 56
- Fat mass (kg)
- 14
Method and assumptions
Lean mass = weight × (1 − body fat fraction). Accuracy depends on the body fat measurement.
Make repeated measurements comparable
A measurement-based estimate can change because the body changed or because the measurement technique changed. Keep the location, units and method consistent when comparing records. The result cannot identify which explanation applies. A ratio or predicted percentage describes only the measurements used by that equation, not a complete assessment of health or fitness.
Common question
Does lean body mass mean muscle mass?
No. Lean body mass includes everything outside the estimated fat mass, including water, organs and bone as well as muscle. The calculator cannot isolate skeletal muscle or tell which component accounts for a change in the result.
Guide updated .