Fat-Free Mass Index (FFMI)
An objective measure of muscularity that scales lean body mass to height, independent of body fat.
Clinical & Bioenergetic Overview
Fat-Free Mass Index (FFMI) is an athletic alternative to BMI. While BMI erroneously classifies muscular athletes as overweight or obese, FFMI isolates fat-free mass and normalizes it to height. In natural, drug-free athletic populations, an FFMI of 19-21 represents average muscularity, 22-23 represents advanced development, and 24-25 represents the upper biological limit of natural muscular potential.
Mathematical Formula & Calculation
Real-World Worked Example
A male standing 1.80m weighing 85 kg at 10% body fat has 76.5 kg of FFM. FFMI = 76.5 / (1.80)² = 76.5 / 3.24 = 23.6 kg/m² (advanced natural muscularity).
Why It Matters for Dieting
Helps lifters identify their remaining genetic ceiling for natural muscle growth and set realistic body composition targets.
Frequent Mistakes
Calculating FFMI using an inaccurate body fat percentage estimate, which skews the resulting score.
Analyze Body Composition
Evaluate your muscular potential and healthy target weight.