Aerostar 19 7/8x21 1/2x1 MERV 6, Fiberglass Air Filter, 19 7/8 x 21 1/2 x 1, Box of 6, Made in the USA Nominal: 19-7/8 x 21-1/2 x 1, Size: 19-7/8"x21-1/2"x3/4" 19 7/8x21 1/2x1, AC Furnace Air Filter Comparable to 3M Filtrete MPR 300 Dust Reduction Fights lint, dust, and pollen. Change frequency 30 days, Made in the USA.