Fat‑Free Mass Index (FFMI)
FFMI (Fat‑Free Mass Index) is a body composition metric that estimates lean tissue (muscle, bone, organs) relative to height. Unlike BMI, it accounts for body fat, giving a clearer picture of muscularity. It is widely used in sports medicine, nutrition, and rehabilitation to monitor muscle gain or wasting.
Formula: FFMI = (weight in kg × (1 – body fat%)) / (height in m)². Values are typically interpreted with gender‑specific ranges. For men: <17 low, 17–19 below average, 19–21 average, 21–23 above average, 23–25 excellent, >25 exceptional (possible doping). For women, subtract ≈2 points (e.g., average 17–19). This calculator provides an instant, evidence‑based interpretation for clinical and fitness settings.
FFMI (Fat-Free Mass Index) is a body-composition metric that estimates how much lean mass (everything that isn’t fat: muscle, bone, organs, water) a person carries relative to height—similar in idea to BMI, but focused on fat-free mass.
Formula
- Fat-Free Mass (FFM) = body weight − fat mass
- FFMI = FFM (kg) ÷ height² (m²)
Because FFMI adjusts for height, it’s often used by clinicians, sports practitioners, and researchers to:
- track changes in lean mass during training, recovery, illness, or weight loss
- support decisions about protein/strength programming
- compare individuals of different heights more fairly than “lean mass in kg” alone
How FFMI is typically estimated
To calculate FFMI you need fat-free mass, which usually comes from a body fat % estimate (e.g., DEXA, BIA scales, skinfolds, BodPod). Since each method has measurement error, FFMI should be treated as a trend tool rather than a perfect “truth number,” especially when comparing across devices.
Interpreting FFMI (practical use)
There isn’t one universal medical cutoff for everyone (it varies with sex, age, ethnicity, training status, and measurement method), but practitioners commonly use broad adult reference bands:
- Men (approx.)
- < 18: lower lean mass
- 18–20: average
- 20–22: above average
- > 22: high (often athletic)
- Women (approx.)
- < 15: lower lean mass
- 15–17: average
- 17–19: above average
- > 19: high (often athletic)
Some practitioners also use “normalized FFMI” (adjusted to a reference height) for comparisons, but for most clinical monitoring, standard FFMI + consistent measurement method is enough.
