FFMI Calculator
Muscularity, normalised for height — like BMI, but for lean mass.
How is FFMI calculated?
FFMI (Fat-Free Mass Index) does for lean mass what BMI does for total weight: it divides your fat-free mass in kg by your height in metres squared, giving a muscularity score that's comparable across different heights. Because taller people naturally carry more lean mass at equivalent relative muscularity, a normalisation adjustment — adding 6.1 × (1.8 − height in metres) — is commonly applied on top of the raw figure, which is what "normalised FFMI" means. It's become a popular reference point in strength and bodybuilding communities for gauging how close someone is to a natural muscular ceiling.
Frequently asked questions
What is a good FFMI?
For natural male lifters, roughly 20-22 is considered a very muscular, near-genetic-ceiling FFMI — the often-cited (and debated) 25 mark is popularly treated as close to the natural limit for most men, with higher scores far more common among enhanced athletes.
How is FFMI different from lean body mass?
Lean body mass is a raw kg figure. FFMI normalises that figure for height, the same way BMI normalises total weight for height — which makes FFMI more useful for comparing muscularity between people of different heights.
Why does FFMI include a height-normalised adjustment?
Taller people naturally carry more lean mass at the same relative muscularity, so a small correction factor (adding 6.1 × (1.8 − height in metres)) is commonly applied to make FFMI comparable across different heights — this calculator includes it.
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