FFMI Calculator
Find out how much muscle you carry for your height — and see how close you are to the natural limit. Enter your stats, get your Fat-Free Mass Index instantly.
FFMI Classification
Where you fall on the muscularity spectrum, based on Kouri et al. 1995 — the most widely cited reference for natural vs. enhanced lifters.
Below Average
Little muscle for your frame. Consistent training will move this up quickly in the first year.
Average
Typical for untrained or lightly-active men. Room for substantial natural growth.
Above Average
Visibly in shape. A few years of consistent lifting usually land people here.
Athletic
Clearly muscular. Dedicated lifters with good programming and diet reach this range.
Very Muscular
Years of serious training. Uncommon in the general lifting population.
Near Natural Limit
The upper edge of what drug-free lifters typically achieve. Rare without exceptional genetics.
Beyond Natural Limit
Kouri 1995 found FFMI > 25 extremely rare in drug-free lifters. Possible but statistically uncommon.
How FFMI is Calculated
Normalizing accounts for the fact that taller lifters naturally accumulate a bit less muscle per unit of squared height. Compare FFMI fairly across heights by using the normalized number — it's the version Kouri used when defining the ~25 natural ceiling.
More Free Tools
Track FFMI from a photo
GainFrame's AI reads your body fat, lean mass, and FFMI from a single progress photo — no measurements, no guesswork.
- FFMI computed automatically on every photo
- See muscle group scores and weak points
- Track changes across weeks and months
- Free to start, no signup required to try
