18x20x1, Filtrete Air Filter, MERV 11, by 3m (Pack of 4) Size: 18" x 20" x 1" Designed with exclusive Filtrete&trade; Brand 3-in-1 technology from 3M to pull in and trap unwanted air particles while letting cleaner air flow through Attracts and captures microscopic particles like smoke and smog and large allergens like pollen from the air passing through the filter Outperforms fiberglass, washable and non-electrostatic 3-month pleated 1" filters For maximum performance, change your filter at least every 90 days