11.8125X19.8125X.75 actual size (12 x 20 x 1 nominal size). This 12x20x1 air filter is an extended surface pleated filter, which outpaces ordinary air filters with medium efficiency, and are engineered for lower pressure drop, and long service life, which reduces HVAC equipment maintenance and energy costs. Our 12x20x1 air filter is graded to ASHRAE test standards 52.2, which establishes that the air filter will operate as good or better than OEM 12x20x1 air filters. Pleated design. MERV graded to ASHRAE grades. 492 cfm flow rate.