Lean mass and FFMI
Works out your lean body mass, fat mass and fat-free mass index (FFMI) from your weight and body fat percentage.
Result
Fill in the fields and the result appears here.
No upper limit or "natural ceiling" threshold is shown here. The figure that circulates for that is a distribution observation from a single sample; it does not describe anyone's ceiling and cannot be used as a target.
How it is calculated
Lean mass is total weight minus fat mass: muscle, bone, organs and water. Not muscle alone — which is why treating every change in lean mass as muscle gain is wrong, especially in the short term where water balance dominates.
FFMI normalises lean mass for height: the same arithmetic as BMI, but the mass in the numerator excludes fat. That exclusion is exactly what BMI fails to do, and why a muscular person shows up as "overweight" there.
Normalised FFMI applies a correction to a 1.80 m reference; raw FFMI is biased in favour of shorter people.
The input to FFMI is a body fat percentage, which is itself an estimate. So this result is a second estimate built on a first one — its error band is wider than the body fat figure it came from.
Sources
- Kouri E.M. ve ark. (1995). Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med 5(4): 223-228.
- VanItallie T.B. ve ark. (1990). Height-normalized indices of the body's fat-free mass and fat mass. Am J Clin Nutr 52(6): 953-959.
You have the number — now comes the decision
Comparing these numbers against weekly data and revising with a stated reason is the actual work. That is how online coaching runs here.