How the fFMI Calculator works
FFMI divides your fat-free mass by height squared, which makes muscularity comparable across heights the way BMI does for weight. The adjusted version normalizes everyone to 1.8 meters, the form used in the research on natural muscular potential.
FFMI = lean mass(kg) ÷ height(m)², adjusted = FFMI + 6.1 × (1.8 − height)
Example: 180 lb at 5 foot 10 and 15% body fat is 69.4 kg lean, an FFMI of about 22, solidly in the clearly-trained range.
Frequently asked questions
What is a natural FFMI ceiling?
The classic study of steroid-era physiques found drug-free athletes clustering under an adjusted FFMI of about 25. It is a strong guideline rather than a hard law; outliers exist.
What FFMI ranges are typical?
Untrained men commonly sit at 17 to 19, consistent lifters 20 to 23, and elite natural physiques 24 to 25. Women run roughly 4 to 5 points lower across the same bands.
Why does FFMI beat scale weight for lifters?
Scale weight cannot tell muscle from fat. FFMI isolates the lean tissue, so a successful recomposition shows up even when the scale barely moves.