FFMI is your fat-free mass in kilograms divided by your height in metres squared. A man of 85 kg, 180 cm and 15% body fat has 72.3 kg of lean mass and an FFMI of 22.3. Scores of 18 to 20 are average, 22 to 23 are excellent, and values above about 25 are rarely reached without anabolic drugs.
What is FFMI?
The fat-free mass index is like BMI, but it only counts lean tissue: muscle, bone, organs and water. The formula is FFMI = (weight × (1 − body fat%)) ÷ height². Because BMI can’t tell muscle from fat, a muscular person can have an “overweight” BMI and a healthy body fat level. FFMI fixes that by removing fat mass from the numerator. It was popularised by a 1995 study of male athletes by Kouri and colleagues, who found that almost all users of anabolic steroids exceeded a normalised FFMI of about 25.
Normalised FFMI
Tall people carry more lean mass for the same index, so researchers normalise to a height of 1.80 m with the formula FFMI + 6.1 × (1.8 − height in metres). The calculator shows both. If you are 1.80 m tall the two figures are identical, and for a taller or shorter person the normalised value is the one to compare with reference tables.
What is a good FFMI?
| Normalised FFMI (men) | Typical interpretation |
|---|---|
| Below 18 | Below average |
| 18 to 20 | Average |
| 20 to 22 | Above average, regular lifters |
| 22 to 23 | Excellent |
| 23 to 25 | Superior, near the natural ceiling |
| Above 25 | Rarely achieved naturally |
For women, the ranges sit roughly three points lower, which the calculator applies when you select female. These are population reference ranges, not a hard natural limit. A few genetically gifted athletes exceed 25 without drugs, and the 1995 data came from a small sample.
The weak spot: measuring body fat
FFMI is only as good as your body-fat estimate. A DEXA scan is accurate to roughly 1 to 3 percentage points, bioimpedance scales and skinfold calipers can be off by 4 to 5. A 5-point error in body fat on a 85 kg person shifts lean mass by about 4 kg and the FFMI by more than one point. For tracking progress, use the same method under the same conditions rather than comparing across methods.
Using FFMI in training
If your FFMI is in the average range, there is room to add muscle with progressive training and enough food. Check your intake with the Calorie Calculator and your Protein Calculator, and benchmark strength with the one-rep max calculator.
How to use this calculator
- Choose metric or imperial units and your sex.
- Enter weight, height and your best estimate of body fat percentage.
- Read the FFMI, the normalised FFMI and the category.
- Re-measure body fat in the same way each time to track changes.
Key figures at a glance
| Formula | lean mass (kg) ÷ height (m)² |
|---|---|
| Normalised | + 6.1 × (1.8 − height in m) |
| Average men | 18 to 20 |
| Rarely natural | Above ~25 |
Frequently asked questions
For men, 20 to 22 is above average and 22 to 23 is excellent. Women are typically about three points lower.
A normalised FFMI around 25 is often cited as the practical limit without steroids, but individuals differ.
BMI uses total weight. FFMI uses lean mass only, so it is far more useful for muscular people.
It depends on how accurately you measure body fat. Errors of a few percent are common with scales and calipers.
Yes, with lower reference ranges. The calculator shifts the categories by three points.