17.5X24.5X.75 actual size (18 x 25 x 1 nominal size). The 18x25x1 air filter is an extended surface pleated filter, which outpaces standard air filters with medium efficiency, and are built for decreased pressure drop, and longer service life, which reduces HVAC equipment maintenance and energy costs. The 18x25x1 air filter is graded to ASHRAE test standards 52.2, which establishes that the air filter will operate as good or better than original manufacturer 18x25x1 air filters. Pleated design. MERV tested to ASHRAE standards. 934 cfm flow rate.