15.5X17.5X.75 actual size (16 x 18 x 1 nominal size). Our 16x18x1 air filter is an extended surface pleated filter, which outpaces standard air filters with medium efficiency, and are engineered for decreased pressure drop, and longer service life, which reduces HVAC equipment maintenance and energy expenses. The 16x18x1 air filter is classified to ASHRAE test standards 52.2, which assures that the air filter will function as good or better than OEM 16x18x1 air filters. Pleated design. MERV classified to ASHRAE classifications. 590 cfm flow rate.