Nominal: 18 x 18 x 1, size: 17 1/2"x17 1/2"x3/4" 18x18x1, ac furnace air filter comparable to 3m filtrete mpr 600 clean living comparable to honeywell micro defense plus fpr 5 fights lint, dust mites, mold spores, pollen, pet dander, and dust. change frequency 60-90 days, made in the usa.
