Homogenization of aluminum extrusion billets facilitates extrusion and improves product quality. In this work, a parameter has been developed that defines the homogenization level of AA6063 extrusion billets. The insoluble α-AlFeSi and β-AlFeSi phases have been experimentally determined by evaluating the length/width ratio of the AlFeSi intermetallic in the microstructure. Using this identification, the area fraction of each phase has been measured. The area fraction of the β-AlFeSi phase in the cast structure is over 65%. In the well-homogenized sample, the β-AlFeSi area fraction decreases to values lower than 20%, while the α-AlFeSi phase ratio increases to over 80%. As the α-AlFeSi percentage in the structure increases, the elongation of the samples steadily increases, from 1% to 24%. Based on the ratio of α-AlFeSi to the entire intermetallic phase, we propose six different homogenization levels. The proposed indexing can be used to define the homogenization state of the billet, regardless of the homogenization temperature and time. The index numbers exhibit a good correlation with the deformation potential of the samples.