FFMI Calculator
Measure your muscle mass relative to your height.
Your result
Enter your details and press calculate to see your result.
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Your Fat-Free Mass Index (FFMI) measures how much muscle you carry relative to your height. It works like Body Mass Index, but instead of using your total weight it uses only your lean mass — everything except fat — so it tells you how muscular you are rather than how heavy. This calculator takes your weight, height and body-fat percentage, strips out the fat to find your lean body mass, and returns both your raw and height-normalised FFMI along with where you sit on a scale from below-average to elite.
How FFMI is calculated
First we find your lean body mass by removing fat: lean mass equals weight times one minus your body-fat percentage. We then divide that lean mass in kilograms by your height in metres squared, the same shape as the BMI formula. Because taller people score lower on this raw value through no fault of their own, we apply a normalisation that adjusts the result to a standard height of 1.8 m, adding 6.1 for every metre you fall short of 1.8. This is the Kouri normalised FFMI, the version most lifters and researchers quote.
For example, a man who weighs 80 kg at 175 cm with 15% body fat has 68 kg of lean mass. Dividing 68 by 1.75 squared (3.06) gives a raw FFMI of 22.2. The normalisation adds 6.1 times the 0.05 m he is below 1.8 m, about 0.3, for a normalised FFMI of 22.5 — a fit, well-muscled figure.
What is a good FFMI?
On the normalised scale, below 18 is under-muscled, 18 to 20 is average, 20 to 22 is fit, 22 to 25 is advanced, and above 25 is elite. Most drug-free men reach a natural ceiling around 25, which is why an FFMI well above that is often taken as a sign of anabolic use. Women score a few points lower across the board because they carry less muscle on average, so read your number against others of the same sex.
Because the index depends on your body-fat figure, an inaccurate body-fat reading throws off the result. A caliper or DEXA estimate gives a far more reliable FFMI than a rough guess. Treat the number as most useful for tracking your own progress: as you add muscle at a steady body fat, your FFMI climbs, which makes it a cleaner measure of training gains than scale weight alone.
FFMI versus BMI
BMI counts all your weight, so a muscular athlete can be flagged as overweight despite carrying little fat. FFMI fixes that blind spot by looking only at lean tissue, which is why it is the better number for anyone who trains. The two are complementary: pair a body-fat measurement with FFMI to separate muscle from fat, and you get a clear picture of body composition that a single bathroom-scale reading can never give.
How to use
- 01
Enter your stats
Add your weight, height and body-fat percentage.
- 02
Calculate
We compute your normalised FFMI.
- 03
Read your level
See where you land from below-average to elite on the scale.
Frequently Asked Questions
Fat-Free Mass Index is like BMI but for lean mass — it shows your muscularity relative to height, normalised to 1.8 m.
Most drug-free men top out around an FFMI of 25; women a few points lower. Higher values are rare without enhancement.
FFMI is built from lean mass, so we first strip out fat using your body-fat percentage.
It reflects muscle relative to height, not health. It is most useful for tracking your own progress over time.
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Last reviewed June 2026 · Methodology & sources