19.5625X19.5625X.75 actual size (20 x 20 x 1 nominal size). This 20x20x1 air filter is an extended surface pleated filter, which exceeds standard air filters with medium efficiency, and are designed for decreased pressure drop, and increased service life, which reduces HVAC equipment maintenance and energy costs. The 20x20x1 air filter is measured to ASHRAE test standards 52.2, which ensures that the air filter will capture debris as good or better than original brand 20x20x1 air filters. Pleated design. MERV rated to ASHRAE standards. 836 cfm flow rate.