Body Composition
Splitting body mass into fat and lean
Once the percentage is known, it applies directly to body mass to give the two components in kilograms.
The Formula
lean mass = weight x (1 - BF% / 100), fat mass = weight - lean mass
Once the percentage is known, it applies directly to body mass to give the two components in kilograms.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| weight | Total body mass | kilograms | For the worked case this is 80 kg. |
| BF% / 100 | Body fat expressed as a fraction | dimensionless | 19.811988411785478% becomes 0.19811988411785478, and 1 minus that is 0.8018801158821452. |
| lean mass | Fat-free mass | kilograms | At 80 kg this is 64.15040927057161 kg, or 141.42744347875959 lb. |
What Each Symbol Means
weightkilograms
Total body mass
For the worked case this is 80 kg.
BF% / 100dimensionless
Body fat expressed as a fraction
19.811988411785478% becomes 0.19811988411785478, and 1 minus that is 0.8018801158821452.
lean masskilograms
Fat-free mass
At 80 kg this is 64.15040927057161 kg, or 141.42744347875959 lb.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate body fat percentage page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Body Fat Percentage, filed under Health. Every number the guide produces comes from substituting into this one line.