Work out fat free mass index instantly with clear inputs, formula shown and shareable results.
FFMI applies the BMI idea to lean mass alone, so it measures muscularity rather than total size. An 80 kg man at 15% fat and 1.78 m carries 68 kg of lean mass, giving an FFMI of 21.5 and a height-normalised 21.6. Values above 25 normalised are very rarely achieved without pharmacological assistance.
Fat-free mass index
FFMI = fat-free mass / height(m)^2
Height normalisation
normalised = FFMI + 6.1 x (1.8 - height in m)
These figures are population-average estimates, not a medical assessment or diagnosis. Body composition equations carry errors of several percentage points, and healthy ranges vary with age, ethnicity, muscularity and medical history. Discuss weight or body composition goals with a qualified clinician or dietitian.
Most drug-free men plateau around 22-23 normalised, with 25 considered the practical natural ceiling in the original Kouri study.
Because the squared denominator still favours shorter people slightly, and the 6.1 correction removes that residual bias.