17.5X21.5X.75 actual size (18 x 22 x 1 nominal size). The 18x22x1 air filter is an extended surface pleated filter, which outpaces ordinary air filters with medium efficiency, and are designed for decreased pressure drop, and increased service life, which reduces HVAC equipment maintenance and energy costs. Our 18x22x1 air filter is rated to ASHRAE test standards 52.2, which establishes that the air filter will function as good or better than original manufacturer 18x22x1 air filters. Pleated design. MERV graded to ASHRAE standards. 811 cfm flow rate.