Before selecting your Furnace Filters Sizes you need to understand the Difference Between Nominal and Actual Size.
Nominal Size is an estimated size rounded up to the nearest inch.
Usually the size of the box where the House Air Filter will fit.
Actual or Exact Size is what the furnace filter dimensions measure exactly.
Example: the Furnace Filters Sizes of our 16x25x4 inches is 15 1/2x 24 1/2x 3 3/4 inches
BE AWARE: They might be a difference in the sizes print on the filter and the exact size. We recommend measuring before shopping for furnace filters sizes.