11.5X17.5X.75 actual size (12 x 18 x 1 nominal size). The 12x18x1 air filter is an extended surface pleated filter, which outperforms ordinary air filters with medium efficiency, and are designed for lower pressure drop, and extended service life, which reduces HVAC equipment maintenance and energy costs. This 12x18x1 air filter is classified to ASHRAE test standards 52.2, which ensures that the air filter will filter as good or better than original brand 12x18x1 air filters. Pleated design. MERV graded to ASHRAE ratings. 443 cfm flow rate.