Actual Size: 17-1/2 x 19-1/2 x 1-3/4 Nominal Size: 18x20x2 Filtration Rating: MERV 10. Comparable to MPR rating 600 to 800, or FPR 5-6 rating. Blocks and Captures: Dust, pollen, mold spores, pet dander, smog, dust mites, debris.