Accumulair Platinum 16x21x1 (15.5x20.5) MERV 11 Air Filter/Furnace Filters (6 pack) Nominal size 16 x 21 x 1, actual size measures 16 x 21 x 0.75 Each filter lasts up to 3 months Uniform pleat shape enhances dust holding capacity and maximizes air flow Supercharged pleated panel filtering media ideally suited for capturing fine airborne allergens such as dust, smoke, dander Merv 11 rating