Lean meat percentage (LMP) is the criterion for carcass classification and it must be measured on line objectively. The aim of this work was to compare the error of the prediction (RMSEP) of the LMP measured with the following different devices: Fat-O-Meat'er (FOM), UltraFOM (UFOM), AUTOFOM and VCS2000. For this reason the same 99 carcasses were measured using all 4 apparatuses and dissected according to the European Reference Method. Moreover a subsample of the carcasses (n=77) were fully scanned with X-ray Computed Tomography equipment (CT). The RMSEP calculated with cross validation leave-one-out was lower for FOM and AUTOFOM (1.8% and 1.9%, respectively) and higher for UFOM and VCS2000 (2.3% for both devices). The error obtained with CT was the lowest (0.96%) in accordance with previous results, but CT cannot be used on line. It can be concluded that FOM and AUTOFOM had better accuracy than UFOM and VCS2000.