Lean Mass & FFMI
Fat-free mass index is BMI with the fat removed — it tells muscle from mass, which BMI cannot.
- 01Enter weight, height and a body-fat percentage.
- 02If you do not know your body fat, estimate it first with the body fat tool.
What the terms mean
- FFMI
- Fat-free mass index: lean mass divided by height squared. BMI with the fat removed.
- Normalised FFMI
- FFMI adjusted to a 1.8 m reference height, so different heights compare fairly.
- Lean mass
- Bodyweight minus fat mass — includes muscle, bone, organs and water.
FFMI needs a body-fat figure. If you don't have one, estimate it first with the body fat tool — the result is only as good as that input.
Above average · normalised to 1.8 m: 21.6
Body fat 15% sits in the Fitness range for your sex. BMI cannot tell muscle from fat; FFMI can, which is why a muscular person often reads as "overweight" on BMI while having a perfectly ordinary FFMI.
Category labels come from population averages and can't tell muscle from fat — a muscular person often lands in a higher band despite low body fat. There is a further limitation worth knowing: the American Medical Association's 2023 position is that BMI correlates with fat mass across a population but loses predictive power when applied to one individual, that its cut-offs derive largely from earlier generations of non-Hispanic white populations, and that it should not be used as a sole measure. Treat this as a rough screening band, not a verdict on your health.
Method & sources
FFMI is lean mass divided by height squared — BMI with the fat removed. The normalised figure adjusts to a 1.8 m reference so people of different heights can be compared. Values around 25 are often cited as an approximate natural ceiling for men, but this comes from a small sample and should be read as a rough guide rather than a hard limit.
Kouri EM, Pope HG, Katz DL, Oliva P, Clin J Sport Med 1995
What these numbers
actually tell you.
What the number means
Roughly: under 18 is below average for men, 18–20 average, 20–22 above average, and above 23 reflects substantial long-term training. Women run several points lower throughout. The value measures all lean tissue, not muscle specifically, so treat it as a proxy.
Why this beats BMI if you train
Two people of identical height and weight, one at 12% body fat and one at 30%, produce the same BMI and very different FFMI. This is the concrete answer to BMI misclassifying athletes. BMI remains reasonable for population screening — it fails specifically at the muscular and sarcopenic extremes.
On the "natural limit" of 25
This traces to a single small 1995 study comparing steroid users and non-users, whose authors did not present it as a hard biological ceiling. Individual variation in frame and genetics is substantial, and the body-fat estimate feeding your FFMI carries several points of error itself. Treat 25 as a loose population observation, not a verdict about any individual.
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