Fit Nutrition library
Lean Body Mass & FFMI Calculator
Estimate lean mass and fat-free mass index.
How it’s calculated
Lean mass is your weight minus fat, then FFMI expresses it relative to height, with a height normalisation.
Lean mass(kg) = weight × (1 − body fat% ÷ 100). FFMI = lean mass ÷ height(m)². Normalized FFMI = FFMI + 6.1 × (1.80 − height m).
Source: Kouri EM, et al., Clinical Journal of Sport Medicine, 1995 (FFMI normalisation).