Abstract The potential drop occurring in the bed of the flow-through porous electrode ( fpe) changes the local metal-solution potential difference ( lpd). Thus it may destroy the considered electrochemical reaction specificity or limit the electrolytic cell efficiency. So, it's necessary to compute the fpe geometry (bed height, particles diameter) which satisfies the lpd for a chosen pair flow-yield. This study, realized in the case of a fixed bed built with very conductive particles, proposes a generalized equations system which permits the fpe design. It's possible to do the same for an undistinguished electrochemical reaction by introducing a characteristic number of this system. From these equations a design diagram is established. A discussion about the axial field electrode limits as performing reactor follows.