It is desirable to have a number that can be used commercially to indicate to consumers the relative operating economy of various sizes, types and brands of household refrigerators. Today domestic refrigerators come in sizes from 8 cu. ft. (.23 m³) to 25 cu. ft. (.7l m³). The amount of this space devoted to the freezer varies from less than one fifth to more than one third. Both of these variables affect the energy consumption of the refrigerator.