For an article of a given type, in particular a garment, a grading mask is used that has images of the pieces of a reference article, geometrical grading regions, each of which contains one or more characteristic points of a piece of the reference article, and grading formulae associated with respective ones of the various regions, each grading formula making it possible, in the associated grading region, and as a function of the variation in one or more magnitudes of a scale of measurements, or of a predetermined increment value, to determine a displacement to be applied to each characteristic point contained in said region for going from the base size to another size. Images of the pieces of the article to be graded for an article size corresponding to the base size of the grading mask are called up, said images are placed on the grading mask in positions corresponding to the positions of the pieces of the mask, and the pieces are graded automatically on the basis of the grading formulae of the mask and of a chosen scale of measurements.