US Home Filter SC40-18X20X1-6 18x20x1 Merv 8 Pleated Air Filter (6-Pack), 18" x 20" x 1" Actual size: 17-3/4 inch x 19-3/4 inch x 3/4 inch Merv 8 tested under ashrae 52.2-2007 standards Ideal for normal air filtration and those with mild allergies Moisture resistant, heavy-duty Frame Galvanized expanded metal backing