Method for determining a semi-finished lens blank, comprising the steps consisting of:—determining, for a given material, a set of faces (S-i , S2, . . . Sn) to be defined for a line of ophthalmic lenses, each face (Si, Sj) being defined for a corresponding subset (SEi, SEj) of wearer data and/or frame data; determining, for each face (Si, Sj), a minimum thickness requirement (EnvSi, EnvSj) necessary to produce all the lenses of the corresponding subset (SEi, SED; determining combinations of two faces (Si, Sj) to be paired; defining a “double-faced” semi-finished lens blank (SF(ij)) consisting of two paired defined faces (Si and Sj) and including the minimum thickness requirements (EnvSi and EnvSj) respectively determined, for said faces, in a manner that allows producing all the lenses of the subsets (SEi and SEj) corresponding to said faces.