19-1/2 x 23-1/2 x 3/4 actual size (20 x 24 x 1 nominal size). Our 20x24x1 air filter is an extended surface pleated filter, which exceeds ordinary air filters with medium efficiency, and are designed for lower pressure drop, and increased service life, which reduces HVAC equipment maintenance and energy costs. The 20x24x1 air filter is governed to ASHRAE test standards 52.2, which establishes that the air filter will capture particulate as good or better than original brand 20x24x1 air filters. Pleated design. MERV tested to ASHRAE grades. 983 cfm flow rate.