What does lean mass include?
In this calculator, lean body mass is used as the common shorthand for fat-free mass. It includes muscle, bone, organs, and water. In precise physiology, lean body mass and fat-free mass can have slightly different definitions.
Subtracting estimated fat mass
Body weight is multiplied by the entered fat percentage to estimate fat mass. The remainder is reported as fat-free mass. This tool does not estimate body-fat percentage from height or weight alone.
How to use this calculator
- 1Enter weight using your preferred unit.
- 2Enter a body-fat percentage from an appropriate measurement or estimate.
- 3Calculate and compare the fat and fat-free portions of total weight.
Understanding your result
The result inherits the uncertainty of the body-fat input. A change in fat-free mass can include changes in water or glycogen, so it should not be reported as the exact amount of muscle gained or lost.
Assumptions & limitations
- Body-fat measurement error directly changes both estimated compartments.
- Hydration changes can affect body weight and many body-composition measurements.
Frequently asked questions
Is lean body mass the same as muscle mass?+
No. The result includes water, bone, organs, and other non-fat tissues in addition to skeletal muscle.
Where can I get a body-fat estimate?+
Circumference methods, skinfolds, bioimpedance, and imaging are possible approaches, each with limitations. The Navy body-fat tool offers a tape-based estimate.
How much does body-fat error affect the result?+
At 80 kg, each percentage point changes estimated fat-free mass by 0.8 kg. An uncertain input can therefore create a meaningful difference.
Can lean mass increase without muscle growth?+
Yes. Water and glycogen shifts can increase measured or estimated fat-free mass without an equivalent increase in muscle tissue.
