Know your body
FFMI calculator
Fat-free mass index is BMI for muscle: lean mass divided by height squared. Unlike BMI, it separates a muscular person from an overweight one — which makes it the most useful single number for tracking how much muscle you carry.
Your numbers
From a DEXA scan, calipers, a smart scale or the tape method.
Your FFMI appears here
Enter height, weight and a body-fat estimate. Everything updates as you type.
How it’s calculated
The formula
Lean mass = weight × (1 − body fat %). FFMI = lean mass (kg) ÷ height (m)². Because raw FFMI creeps up with height even at equal muscularity, Kouri et al. (1995) proposed a height-normalised version: FFMIₙ = FFMI + 6.1 × (1.8 − height in m). We show both and use the normalised figure for comparisons.
Where the reference bands come from
Kouri’s study of 157 male athletes found drug-free lifters clustered below a normalised FFMI of about 25, with a mean near 22 in trained men. Female data is thinner; values around 16–17 are typical and 20+ is exceptional. Bands on this page are descriptive, not diagnostic.
Limitations
FFMI is only as good as the body-fat estimate behind it. A body-fat reading that is 4 points too low inflates FFMI by roughly 1 point. It also counts water, organs and bone as “fat-free mass”, so it measures muscularity indirectly.
Full sources and limitations are on the methodology page. Estimates are for healthy adults and are not medical advice.
Questions
What is a good FFMI?
For men, 19–20 is average among untrained adults, 21–22 reflects years of consistent training, and 23–25 is advanced. For women, subtract roughly 3–4 points.
Is an FFMI over 25 proof of steroid use?
No. It is rare among drug-free lifters, but body-fat estimation error, unusual genetics and measurement at peak pump all push numbers up. Treat it as “unusual”, not “proof”.
Should I use FFMI or normalised FFMI?
Use normalised FFMI when comparing yourself with other people or with reference ranges. Either works for tracking yourself over time, as long as you are consistent.