20x25x4 Air Filter: Actual Size, MERV Picks, and Where to Buy
Nominal size (what you shop by)
20x25x4
- Actual size
- 19.5 x 24.5 x 3.63
- Replace
- Typically every 6 to 12 months
Actual size shown is from Filterbuy for a standard 4 inch pleated filter. Honeywell media cabinets labeled 20x25x4 take a deeper filter (about 19.88 x 24.75 x 4.38) that Filterbuy sells as 20x25x5. Check your cabinet brand before you buy.
Check three things before you buy
- The thickness (the last number) matches your filter slot.
- The size matches the label on your current filter, or your measurements.
- The MERV rating is one your system's manual allows.
Picking a MERV rating
- MERV 8: Standard household filtering. Catches dust, pollen, and lint.
- MERV 11: A step up for pets and allergies. A common upgrade.
- MERV 13: Catches much smaller particles. Check your system's manual first, because tighter filters can restrict airflow.
Buy the right one
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Common questions
What is the actual size of a 20x25x4 filter?
Commonly 19.5 x 24.5 x 3.63, but it varies slightly by brand.
What is the difference between nominal and actual size?
The nominal size (20x25x4) is the rounded name used when you shop. The actual size is usually a little smaller so the filter slides in easily, and it can vary slightly by brand. Check the package for the exact measurements.
How often should I replace it?
Typically every 6 to 12 months. Replace sooner with pets, allergies, or heavy use, and follow your system's manual.
Source: manufacturer documentation
Not sure of your size? How to measure your filter.