FFMI Calculator: Fat-Free Mass Index
Gauge how much muscle you carry for your height, with the height-adjusted index from the original research.
- 2 cited sources
- Calculates in your browser
Your answer
Appears here as you enter your details. No demo figures — the number is yours, or it is nothing.
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The fat-free mass index normalises muscle mass to height:
FFMI = fat-free mass (kg) ÷ height (m)², with
fat-free mass = weight × (1 − body fat ÷ 100)
Because raw FFMI drifts slightly with height, we also show the
height-adjusted FFMI from the original paper:
adjusted = FFMI + 6.1 × (1.8 − height in m).
The metric comes from Kouri and colleagues' 1995 study comparing steroid users and non-users: among 157 athletes, drug-free FFMI clustered below ~25 while users commonly exceeded it.
Interpreting your result
As rough bands for men: 17 to 20 spans typical untrained to recreationally trained physiques, 20 to 23 reflects serious training, and 23 to 25 approaches the drug-free ceiling observed in the research. Women average roughly 2.5 to 3 points lower. FFMI is best used to track your own trajectory, gaining a point of FFMI at stable body fat is a meaningful year's work for an experienced lifter.
Limitations
- Your FFMI is only as good as your body-fat estimate: ±3 percentage points of body-fat error moves FFMI by about ±1 point.
- The 25 "limit" is a statistical observation from one cohort, not a law of biology, genetic outliers exist.
- FFMI says nothing about strength, performance or health; it is a body-composition description only.
Sources
Pull the receipts, 2 cited sources
Frequently asked questions
- What is a good FFMI?
- Around 18 to 20 is typical for untrained men, 20 to 22 reflects serious training, and values above roughly 25 were rare among drug-free athletes in the original research. Women average about 2.5 to 3 points lower.
- Is 25 FFMI really a natural limit?
- It's a statistical observation, not a law. In Kouri's sample of drug-free bodybuilders, FFMI rarely exceeded 25. Outliers exist, but the further above 25, the rarer the physique.
- Why adjust FFMI for height?
- Raw FFMI drifts slightly downward for taller people. The published adjustment (+6.1 × (1.8 − height in metres)) normalises everyone to a 1.8 m reference, making comparisons fairer.
- How accurate is my FFMI?
- Exactly as accurate as your body-fat estimate, since errors pass straight through. A ±3-point body-fat error moves FFMI by roughly ±1 point.
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