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Fat-Free Mass Index (FFMI) Calculator

Calculate FFMI and height-normalized FFMI from weight, height, and body fat percentage using the Kouri formula.

Fat-free mass
69.7 kg
FFMI
22
Normalized FFMI (at 1.8m / 5'11")
22.1

How it works

Fat-Free Mass Index (FFMI), introduced by Kouri et al. (1995), measures muscularity in a way that accounts for height: FFMI = fat-free mass(kg) ÷ height(m)², where fat-free mass = weight × (1 − body fat% ÷ 100). Two people with the same body fat percentage but different heights can have very different amounts of muscle, so a taller person's raw FFMI runs higher for the same relative leanness.

To make FFMI comparable across heights, the same study defined a normalized version: normalized FFMI = FFMI + 6.1 × (1.8 − height in meters). This rescales every result to what it would be at a reference height of 1.8m (about 5'11") — someone shorter than that gets a small upward adjustment, someone taller a small downward one.

Body fat percentage is an input you supply from another method — a skinfold test, bioelectrical impedance scale, DEXA scan, or this site's own Navy body fat calculator — this calculator doesn't estimate body fat itself, only what FFMI it implies.

FAQ

What counts as a high FFMI?

Kouri's original study found that drug-free male bodybuilders rarely exceeded a normalized FFMI of about 25, which is why that number is often cited informally as a rough upper bound for natural muscularity. It's not a hard ceiling — genetics, training history, and measurement error all shift where any individual falls — and the study's data was male-only, so the same reference point doesn't transfer directly to women.

Why does the calculator need body fat percentage as an input instead of estimating it?

FFMI is only as accurate as the body fat percentage you provide, and different measurement methods (skinfolds, impedance scales, DEXA) can disagree by several percentage points for the same person. Rather than silently picking one estimation method and presenting it as fact, this calculator takes your own best available number and does the FFMI arithmetic on it.

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