What is FFMI?
Fat-free mass index (FFMI) measures how much lean mass — muscle, bone, organs and water — you carry for your height. It works like BMI but ignores fat, so it separates a muscular person from someone who is simply heavy.
How FFMI is calculated
Lean mass = weight × (1 − body fat %)
FFMI = lean mass (kg) ÷ height (m)²
Normalized FFMI = FFMI + 6.1 × (1.80 − height in m)
The normalization comes from Kouri et al. (1995). It adjusts everyone to a height of 1.80 m, because taller people carry more lean mass per square metre and would otherwise score higher.
FFMI chart for men
| Normalized FFMI | Rule-of-thumb level |
|---|---|
| Under 18 | Below average |
| 18–20 | Average |
| 20–22 | Above average |
| 22–23 | Excellent |
| 23–25 | Superior (near the drug-free limit Kouri observed) |
| 25 and above | Above the drug-free maximum Kouri observed (25) |
What each FFMI is in kilograms of muscle
The bands above tell you whether a number is good. They do not tell you what it is. FFMI is lean mass divided by height squared, so the same figure is a different amount of muscle on a different person — and until you see it in kilograms, “23” is just a number.
Find your normalized FFMI down the left and your height across the top. The cell is the lean mass — muscle, bone, organs and water, everything that is not fat — that figure represents.
| Normalized FFMI | Level | 160 cm | 165 cm | 170 cm | 175 cm | 180 cm | 185 cm | 190 cm |
|---|---|---|---|---|---|---|---|---|
| 17.0 | Below average | 40.4 kg | 43.8 kg | 47.4 kg | 51.1 kg | 55.1 kg | 59.2 kg | 63.6 kg |
| 17.5 | Below average | 41.7 kg | 45.2 kg | 48.8 kg | 52.7 kg | 56.7 kg | 60.9 kg | 65.4 kg |
| 18.0 | Average | 43.0 kg | 46.5 kg | 50.3 kg | 54.2 kg | 58.3 kg | 62.6 kg | 67.2 kg |
| 18.5 | Average | 44.2 kg | 47.9 kg | 51.7 kg | 55.7 kg | 59.9 kg | 64.4 kg | 69.0 kg |
| 19.0 | Average | 45.5 kg | 49.2 kg | 53.1 kg | 57.3 kg | 61.6 kg | 66.1 kg | 70.8 kg |
| 19.5 | Average | 46.8 kg | 50.6 kg | 54.6 kg | 58.8 kg | 63.2 kg | 67.8 kg | 72.6 kg |
| 20.0 | Above average | 48.1 kg | 52.0 kg | 56.0 kg | 60.3 kg | 64.8 kg | 69.5 kg | 74.4 kg |
| 20.5 | Above average | 49.4 kg | 53.3 kg | 57.5 kg | 61.8 kg | 66.4 kg | 71.2 kg | 76.2 kg |
| 21.0 | Above average | 50.6 kg | 54.7 kg | 58.9 kg | 63.4 kg | 68.0 kg | 72.9 kg | 78.0 kg |
| 21.5 | Above average | 51.9 kg | 56.0 kg | 60.4 kg | 64.9 kg | 69.7 kg | 74.6 kg | 79.8 kg |
| 22.0 | Excellent | 53.2 kg | 57.4 kg | 61.8 kg | 66.4 kg | 71.3 kg | 76.3 kg | 81.6 kg |
| 22.5 | Excellent | 54.5 kg | 58.8 kg | 63.3 kg | 68.0 kg | 72.9 kg | 78.1 kg | 83.4 kg |
| 23.0 | Superior | 55.8 kg | 60.1 kg | 64.7 kg | 69.5 kg | 74.5 kg | 79.8 kg | 85.2 kg |
| 23.5 | Superior | 57.0 kg | 61.5 kg | 66.2 kg | 71.0 kg | 76.1 kg | 81.5 kg | 87.0 kg |
| 24.0 | Superior | 58.3 kg | 62.8 kg | 67.6 kg | 72.6 kg | 77.8 kg | 83.2 kg | 88.8 kg |
| 24.5 | Superior | 59.6 kg | 64.2 kg | 69.0 kg | 74.1 kg | 79.4 kg | 84.9 kg | 90.6 kg |
| 25.0 | Above the drug-free maximum Kouri observed | 60.9 kg | 65.6 kg | 70.5 kg | 75.6 kg | 81.0 kg | 86.6 kg | 92.5 kg |
| 25.5 | Above the drug-free maximum Kouri observed | 62.2 kg | 66.9 kg | 71.9 kg | 77.2 kg | 82.6 kg | 88.3 kg | 94.3 kg |
| 26.0 | Above the drug-free maximum Kouri observed | 63.4 kg | 68.3 kg | 73.4 kg | 78.7 kg | 84.2 kg | 90.0 kg | 96.1 kg |
Read down a column and the cost of a point becomes obvious: at 180 cm, every whole point of FFMI is about 3.2 kg of lean mass. Going from 20 to 23 is roughly ten kilograms of it, which is years rather than months of training. That is the honest context for the natural-limit number below.
The FFMI natural limit
Kouri and colleagues measured 157 male athletes, 83 of whom had never used steroids. The drug-free group averaged a normalized FFMI of about 21.8, and none exceeded 25.0; many steroid users did. That is where the widely quoted “natural limit of 25” comes from. Treat it as a reference, not a verdict: body-fat measurement error alone can move FFMI by a point.
FFMI for women
Women carry less lean mass on average, so typical FFMI values run about 3–4 points lower than men's. Research on female upper limits is limited, so we don't show categories for women.
Estimating body fat
DEXA scans are the most practical accurate option. Smart scales and skinfold calipers are convenient but can be off by several percent, which shifts FFMI. Use the same method each time and focus on the trend.
Frequently asked questions
What is a good FFMI?
For men, a normalized FFMI of 18–20 is typical of untrained people, 20–22 shows clear training, and 22–25 is advanced. Women typically score about 3–4 points lower. The categories are a rule of thumb, not medical standards.
Is an FFMI of 25 really the natural limit?
In Kouri et al. (1995), none of the 83 drug-free male athletes studied exceeded a normalized FFMI of 25.0, while many steroid users did. It is a useful reference point, not a hard rule: a small number of people, and measurement error in body fat, can push results slightly above it.
What is the difference between FFMI and normalized FFMI?
Taller people naturally carry more lean mass per square metre, so normalized FFMI adjusts everyone to a height of 1.80 m by adding 6.1 × (1.80 − your height in metres). Use normalized FFMI to compare people of different heights.
How accurate is my FFMI?
FFMI is only as accurate as your body-fat estimate. A 3% error in body fat changes FFMI by about 0.7 points for an average man, so a DEXA scan gives a more reliable result than a mirror estimate.
Sources
The formula on this page comes from the published work below. We check the numbers against the worked examples in these sources with automated tests, and re-read the page against them when we review it.
- Kouri EM, Pope HG Jr, Katz DL, Oliva P. Fat-free mass index in users and nonusers of anabolic-androgenic steroids. Clin J Sport Med. 1995;5(4):223–228. pubmed.ncbi.nlm.nih.gov/7496846/
General fitness information, not medical advice. Results are estimates; check with a doctor or qualified coach before major changes to diet or training. Formula and copy last reviewed 11 November 2026.