Fat-Free Mass Index measures lean mass relative to your height, the same way BMI measures weight relative to height. It is the closest thing to an honest answer for how much muscle you actually carry.
Enter your weight, height, and body fat percentage for an instant FFMI. Add wrist and ankle measurements for frame-size context on top of the population category.
The three inputs FFMI actually needs.
Unlocks frame-size context on top of the population category.
Against real natural-lifter benchmarks, not guesswork.
No hidden tiers. Start free, upgrade only when you want deeper analysis.
Enter your weight, height, and body fat percentage, an honest estimate is fine, this tool is only as useful as your inputs.
FFMI is lean mass divided by height squared, height-normalized using the Kouri et al. 1995 constant so the number compares fairly across different heights. This is the same formula and category bands used across every AadiFit tool that reports FFMI.
FFMI tells you how much muscle you carry relative to your frame, not how you look.
Recalculate every 8-12 weeks during a dedicated muscle-building phase.
Fat-Free Mass Index takes your lean body mass, weight minus fat mass, and normalizes it for height the same way BMI normalizes total weight. That height adjustment matters: a 200cm lifter and a 165cm lifter can carry very different absolute amounts of muscle and still be equally developed relative to their frame. FFMI was developed by Kouri, Pope, Katz, and Oliva in 1995 specifically to compare muscularity fairly across different heights, and to give natural bodybuilding research a consistent yardstick.
Kouri's original research on natural and steroid-using bodybuilders found that drug-free lifters essentially never exceeded an FFMI of 25, while enhanced lifters routinely did. That is not a hard physiological wall, some genetic outliers land higher naturally, but it is a well-corroborated statistical reference point still cited across natural bodybuilding research today. If your FFMI reads above 25, treat that as a prompt to double-check your body fat estimate before anything else, since FFMI is only as accurate as the input feeding it. Cross-check with the Body Composition Analyzer, which uses the identical formula so the two numbers will always agree.
Wrist and ankle circumference are established proxies for skeletal frame size, those joints carry almost no muscle or fat, so their size reflects bone structure more than training history. A larger frame generally supports more lean mass at the same relative development. Several individualised formulas exist that try to convert frame size into a precise weight ceiling, we deliberately don't quote one here, the versions in circulation trace back to inconsistent sourcing and we would rather tell you that honestly than hand you a confident-sounding number we can't verify. Frame size shifts your realistic range, it does not fix an exact target.
FFMI moves slowly because it requires building real lean mass, not water weight or a good pump. The inputs that matter are the same as any hypertrophy program: progressive overload over months, adequate protein, and a calorie surplus sized to your training age, aggressive surpluses mostly add fat, not FFMI. Pair this tool with the Workout Generator to structure the training side and the Calorie Planner to set a surplus that supports growth without excess fat gain.