Nominal vs. Actual HVAC Filter Size
A filter sold as 20x25x1 is usually slightly smaller than those exact dimensions. The rounded label is the nominal size; the precise measurement is the actual size.
Fit rule: The full appliance model and printed replacement part number take priority over appearance alone.
Read both labels
Many filters print the nominal size in large type and actual dimensions in smaller type.
Measure the existing filter
Measure length, width, and depth. A fraction of an inch can determine whether the filter slides into the rack.
Check airflow guidance
A higher MERV rating can increase resistance. Follow the HVAC manufacturer or technician guidance for your system.