A method is outlined for correlating experimental data obtained in studies of the flow of gases and liquids through porous metals. The correlation is based upon the suggestion of Forcheimer that the pressure gradient attending the flow of a liquid through a porous medium can be expressed as a function of flow rate by a simple quadratic equation. An equation of this type defines two length parameters necessary for characterization of a porous structure and permits a general definition of the Reynolds number for a structure of arbitrary complexity.