FFMI Calculator

Your weight tells you almost nothing on its own. FFMI fixes that. It strips out fat and rates the muscle you carry against your height, so a lean 80 kg lifter and a soft 80 kg one get different scores. Enter your weight, height and body fat above and the calculator returns both your raw FFMI and the height-normalized version.

What FFMI measures

FFMI is fat-free mass divided by height squared. It is the muscle-focused cousin of BMI. Where BMI punishes you for carrying muscle, FFMI rewards it. The number answers one question: for your frame, how much lean mass are you carrying?

The calculation needs an honest body fat figure. If you do not have one, measure it first with the body fat calculator, then come back. A guessed body fat will swing your FFMI by a couple of points.

The natural ceiling

Normalized FFMI matters because of one well-known landmark. A study of drug-free and steroid-using lifters found that almost no natural athlete exceeded a normalized FFMI of around 25. That figure has held up as a rough natural limit ever since.

Read it as a soft ceiling, not a wall. Genetics, low body fat readings, and measurement error all move it. If your number lands above 25, the first thing to check is your body fat input, since a too-low reading inflates lean mass.

Using it to train

Track FFMI over months, not weeks. Muscle is slow. A natural lifter adding mass might move their FFMI by a point or two across a focused year. Retest every few months at the same body fat range so you are comparing like with like.

To turn this into a plan that adds lean mass while holding body fat, read the body recomposition guide.