Actual Size: 19-1/2 x 24-1/2 x 3-3/4 Nominal Size: 20x25x4 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.