1. A method of automatically grading an article of a given type, in particular an article of a garment type, that is formed by assembling a plurality of pieces, said method comprising: using a grading mask having images of the pieces of a reference article of the same type as the type of the article to be graded and for a given base size, a plurality of 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; calling up the images of the pieces of the article to be graded for an article size corresponding to the base size of the grading mask; placing the images of the pieces of the article to be graded on the grading mask in positions corresponding to the positions of the pieces of the mask; and automatically grading the pieces of the article to be graded on the basis of the grading formulae of the mask and of a chosen scale of measurements for the article to be graded.