Fat-Free Mass Index (FFMI) measures muscularity relative to height. Here's how it's calculated and what the numbers mean.
FFMI takes your lean body mass and divides it by height squared, then normalizes the result to a 1.8m reference height so people of different heights can be compared fairly. It's often used to gauge how much natural muscle-building potential someone has reached.
| FFMI | Interpretation |
|---|---|
| Below 18 | Below average |
| 18–20 | Average |
| 20–22 | Above average / muscular |
| 22–23 | Very muscular |
| 23–25 | Exceptional (near natural limit) |
| 25+ | Rare without performance-enhancing drugs |
Natural FFMI ceilings are typically lower for women, often topping out in the high teens to low twenties.
FFMI depends heavily on an accurate body fat percentage input — small errors there shift the result noticeably. It's best used as a rough benchmark over time rather than a precise, one-time measurement.
See how your muscularity compares to natural benchmarks.
Open FFMI CalculatorFor men, a normalized FFMI of 20–22 is considered good, and above 25 is rare without performance-enhancing drugs.
FFMI measures muscle mass relative to height, giving a sense of how muscular someone is independent of total body weight.
Yes — body fat percentage is used to separate lean mass from fat mass before calculating the index.
Last Updated: July 2026