FFMI Calculator
Fat-Free Mass Index -- a height-normalized measure of lean mass, popularized as a rough, population-level ceiling check on natural muscularity.
An estimate is fine -- FFMI is only as precise as this number, which caliper or scale body-fat readings rarely pin down exactly.
FFMI (raw)
22.0
Normalized FFMI
22.1
Adjusted to a 5'11" (1.8 m) reference height
How it's calculated
Lean mass divided by height squared, then height-corrected:
Normalized FFMI = FFMI + 6.1 × (1.8 − height(m))
From Kouri, Pope, Katz & Oliva (1995), "Fat-free mass index in users and non-users of anabolic-androgenic steroids," Clinical Journal of Sport Medicine.
Worked example: 200 lb (90.7 kg), 5'11" (1.803 m), 15% body fat
Raw FFMI: 23.7. At 5'11" the height correction is nearly zero, so the normalized score, 23.7, lands almost identical to the raw number. Enter these same numbers above and the tool matches.
Frequently Asked Questions
What does FFMI actually measure?
How much fat-free (mostly muscle) mass you're carrying relative to your height, squared -- the same shape of formula as BMI, but built from lean mass instead of total bodyweight. It says nothing about your body fat percentage on its own; two people with identical FFMI can look very different if one carries noticeably more fat.
Why does FFMI need to be "normalized"?
Because dividing by height squared structurally penalizes taller people -- a 6'4" and a 5'6" lifter with proportionally identical builds land on different raw FFMI numbers. The normalized version adds a correction (6.1 x (1.8 - height in meters)) so both land on a comparable scale, referenced to 5'11" (1.8 m).
Where does the "natural limit" idea around FFMI come from?
Kouri, Pope, Katz and Oliva's 1995 study in Clinical Journal of Sport Medicine found normalized FFMI scores above roughly 25 were rare among steroid-free bodybuilders in their sample and common among steroid users. It's a population-level observation from one study's sample, not a hard physiological ceiling -- some steroid-free lifters do exceed it, especially with favorable genetics and long training histories.
How accurate is this without a real body-fat measurement?
Only as accurate as the body fat percentage you enter. A caliper, scale, or visual estimate all carry real error margins (often several percentage points), and that error carries straight through into the FFMI result -- treat the output as a rough estimate, not a lab-grade number.
Keep going
- FFMI is built directly on your lean mass; see three separate published formulas estimate that number here. Lean Body Mass Calculator
- FFMI rates how much muscle you're carrying; strength standards rate what you can actually lift with it. Strength Standards