Fat-Free Mass Index (FFMI) Calculator
Turn your weight, height and body-fat percentage into a fat-free mass index (FFMI) and a height-normalized FFMI to gauge how much muscle you carry for your frame.
How it works
FFM = weight·(1 − bodyfat%/100) · FFMI = FFM ÷ height(m)² · normalized FFMI = FFMI + 6.1·(1.8 − height in m)
Fat-free mass index answers a question BMI cannot: how much lean tissue do you carry relative to your height? It divides your fat-free mass by height squared, so two people of the same height can be compared directly. The normalized version adjusts to a reference height of 1.8 m so tall and short lifters are on the same scale. A normalized FFMI near 25 is the widely quoted upper edge of what most people reach without performance-enhancing drugs, though genetics move that line.
Worked example
An 80 kg, 1.80 m person at 15% body fat has FFM = 80·0.85 = 68 kg, FFMI = 68 ÷ 1.8² = 68 ÷ 3.24 = 21.0, and because height is exactly 1.8 m the normalized FFMI is also 21.0 — an above-average but natural figure.
Sources: Kouri E. et al. — FFMI in users and nonusers of anabolic steroids (PubMed)
Frequently asked questions
What FFMI is achievable naturally?
Most drug-free trainees top out around a normalized FFMI of 22–25, with about 25 often cited as a practical ceiling. Individual genetics, training age and measurement error all shift this, so treat it as a guide rather than a hard limit.
Why normalize to 1.8 m?
Raw FFMI slightly favors shorter people, so the normalization adds a small correction that brings everyone to a common 1.8 m reference height. It makes comparisons between people of different heights fairer.
Do I need an accurate body-fat number?
Yes — FFMI is only as good as the body-fat percentage you feed it. A skinfold or DEXA estimate is far better than a guess, since a few points of error move FFMI by a full unit.
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Educational estimate, not medical advice — for personal health decisions consult a qualified healthcare professional.