Filter King Merv 8 25.5x42x1 4-Pack Air Filter actual size is 25.5x42x1.75. Our 25.5x42x1 Furnace Filters are designed to last up to 90 days. These pleated 1-inch air filters are ideal for maintaining the efficiency of your heating and cooling systems. Make sure you measure your filter. The actual size of this pleated Merv 8 filter is 25-1/2 x 42 x 1-3/4