By Zencalcy Editorial TeamLast reviewed About us
Fat-Free Mass Index (FFMI) expresses how much lean tissue you carry relative to your height. It is similar to BMI but removes fat mass from the numerator, so it is more useful for comparing muscularity between people. Normalised FFMI adjusts the value to a 1.8 m reference height.
Normalise fat-free mass for height and compare with reference ranges.
FFM(kg) = weight × (1 − body fat % ÷ 100) FFMI = FFM ÷ height(m)² Normalised FFMI = FFMI + 6.1 × (1.8 − height(m))
FFMI is only as good as the body-fat input. DEXA, hydrostatic weighing or a skilled skinfold assessment are more reliable than a bathroom scale. Reference ranges are descriptive and were developed largely in male lifting populations.
| Symbol | Meaning |
|---|---|
| FFM | Fat-free mass in kilograms. |
| FFMI | Fat-free mass divided by height squared. |
| Normalised FFMI | FFMI adjusted to a 1.8 m reference height. |
FFM = 80 × 0.85 = 68 kg. FFMI = 68 ÷ 1.8² = 20.99. Height is already 1.8 m, so normalised FFMI is also 20.99, near the top of the average range for men.
BMI treats muscle and fat as the same kilogram. That is why a lean, muscular athlete and a sedentary person of the same height can share a BMI while having very different body composition. FFMI separates the two by subtracting fat mass first. The normalisation step matters because height is squared in the denominator, so a 1.95 m athlete would otherwise look less muscular than a 1.70 m athlete with the same absolute lean mass. Even normalised, FFMI has limits. It depends on an accurate body-fat measurement, and it does not distinguish where lean mass sits or how strong it is. A person with a high FFMI from years of training and a person with a high FFMI from a very large frame can look the same on paper. Use it to track changes in lean mass over time, not as a scoreboard for worth or health.
Continue with the ABSI Calculator (A Body Shape Index), Adjusted Body Weight Calculator, or the BAI Calculator (Body Adiposity Index) — or browse more body measurements tools and all health calculators.
Also see the Body Fat Calculator.
For men, values around 18–20 are average, 20–22 above average, 22–23 excellent and above 23 exceptional. For women, typical ranges are lower: about 15–17 average, 17–19 above average and 19–21 excellent. These are descriptive, not targets.
Every result is a screening estimate from published anthropometric equations, not a diagnosis or a measurement of body composition. Tape measurements should be taken snugly against the skin without compressing it, at the landmarks named in each tool. Equations were derived in specific populations and can be less accurate for athletes, older adults, children, pregnant people and people with significant oedema.
Reference material used to build and check this calculator:
Last reviewed: September 2026. See how we build and check every tool on the about page.
Content updated: September 2026