FFMI Calculator — Fat-Free Mass Index

Gauge how much muscle you carry for your height, with the height-adjusted index from the original research.

  • Nutrition
  • 2 cited sources
  • Runs in your browser
Unit system

Your fat-free mass index

21.0

Height-adjusted: 21.0 · fat-free mass 68.0 kg

Typical untrained men sit around 18–20; values above ~25 were rare among drug-free athletes in the original research. Accuracy depends entirely on your body-fat estimate.

Methodology

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: 17–20 spans typical untrained to recreationally trained physiques, 20–23 reflects serious training, and 23–25 approaches the drug-free ceiling observed in the research. Women average roughly 2.5–3 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

FitTools · sources

  1. 01 Kouri EM, Pope HG, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med 1995;5:223–228
  2. 02 Hodgdon JA, Beckett MB. Naval Health Research Center Report 84-11, 1984 (body-fat input method)

Every formula cited ✓

Frequently asked questions

What is a good FFMI?
Around 18–20 is typical for untrained men, 20–22 reflects serious training, and values above roughly 25 were rare among drug-free athletes in the original research. Women average about 2.5–3 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 — errors pass straight through. A ±3-point body-fat error moves FFMI by roughly ±1 point.

Written and reviewed by Mathew Beale — MSc Biotechnology, University of Reading.

Last reviewed:

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