US Home Filter SC60-18X18X1-6 18x18x1 Merv 11 Pleated Air Filter (6-Pack), 18" x 18" x 1" Actual size: 17-3/4 inch x 17-3/4 inch x 3/4 inch Merv 11 tested under ashrae 52.2-2007 standards Ideal for those with moderate allergies Moisture resistant, heavy-duty Frame Galvanized expanded metal backing