Accumulair Diamond 20x21x1 (Actual Size) MERV 13 Air Filter/Furnace Filters (6 pack) Actual Size Measures 20 x 21 x 0.75 Great for helping reduce airborne allergens such as bacteria, particles that carry viruses, pollen, mold spores, fine dust, and pet dander. Each filter lasts up to 3 months. Electrostatically charged filter media captures airborne allergens smaller than 1 micron! MERV 13 Rating