A computational fluid dynamic (CFD) analysis was used as a useful tool to obtain numerical relationships among similar flow-field designs having different active areas. Assuming that, at fixed current density, the porous layer velocity distribution calculated for the smallest size geometry was the optimal, a scale-up methodology has been proposed and implemented in software. It allows acquisition of the scaled-up flow-field by multiplying the reference cell parameters by suitable factors (scale factors). A calibration methodology has also been proposed by the introduction of a feedback factor evaluated by CFD analysis. A first application of this procedure has been carried out to scale-up a 5–125 cm 2 cell.