Nominal Size: 21 1/2 x 23 3/8 x 1, Actual Size: 21 1/2' x 23 3/8' x 3/4', 21 1/2x23 3/8x1, AC and Furnace Air Filter Comparable to MPR 1000 to 1200 Micro Allergen Defense Comparable to Honeywell Allergen Plus FPR 7 Designed to filter microscopic particles such as lint, dust mites, spores, pollen, pet dander, dust, and smoke. Change frequency 60-90 days, Made in the USA.