11-1/2 x 23-1/2 x 3/4 actual size (12 x 24 x 1 nominal size). This 12x24x1 air filter is an extended surface pleated filter, which outperforms standard air filters with medium efficiency, and are built for decreased pressure drop, and increased service life, which reduces HVAC equipment maintenance and energy expenses. The 12x24x1 air filter is measured to ASHRAE test standards 52.2, which ensures that the air filter will perform as good or better than OEM 12x24x1 air filters. Pleated design. MERV classified to ASHRAE classifications. 590 cfm flow rate.