What is FFMI?
FFMI = lean mass (kg) ÷ height² (m²). A height-normalised version adds a correction factor of 6.1 × (1.8 − height in metres) so that taller and shorter individuals can be compared on a common scale.
FFMI Calculator
Calculate your Fat-Free Mass Index (FFMI) to gauge muscularity relative to your height, with a normalised score and category from below average to exceptional.
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Sex
Units
Above average
21.5
FFMI
21.6
Normalised FFMI
68 kg
Fat-free mass
| FFMI | 21.5 |
| Normalised FFMI (height-adjusted) | 21.6 |
| Fat-free mass | 68 kg / 149.9 lbs |
| Category | Above average |
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Body Composition
FFMI Calculator — Fat-Free Mass Index
The Fat-Free Mass Index (FFMI) measures muscularity relative to height, independent of body fat. It is calculated as lean body mass in kilograms divided by height in metres squared, and is commonly used to gauge how much muscle a person carries relative to their frame.
How to calculate lean mass
Lean body mass = total body weight × (1 − body fat% / 100). You will need an estimate of your body fat percentage — from a Navy calculator, bioelectrical impedance scale, or DEXA scan. A more accurate body fat input produces a more accurate FFMI.
FFMI reference ranges
Research by Kouri et al. (1995) found that non-enhanced (drug-free) athletes historically scored below 25 in normalised FFMI. Scores above 25–26 are considered exceptional and overlap with the range commonly seen in enhanced athletes. For women, typical natural upper limits are approximately 2–3 points lower.
Limitations
FFMI is a tool for broad comparison, not an individual ceiling or goal. Genetics, training age, measurement accuracy, and testing conditions all affect the result.
Frequently asked questions
Most research places the natural upper limit for men at around 25 (normalised). Scores of 22–25 are considered excellent and athletic. For women, 19–22 is in the same excellent range.
Use the most accurate measurement you have. DEXA is the gold standard, followed by hydrostatic weighing, then skinfold calipers and circumference methods.
Normalisation adds 6.1 × (1.8 − height in metres), making cross-height comparisons fair. A 1.70 m person and a 1.90 m person with identical physiques get the same normalised score.
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