Compare common home HVAC, furnace and AC filter sizes before buying a replacement.
Quick Answer
Common home air filter sizes include 16x20x1, 16x25x1, 20x20x1, 20x25x1, 16x25x4 and 20x25x4. The printed nominal size is often slightly larger than the measured actual size.
Nominal Size Helper
Common Sizes
| Nominal size | Typical actual clue | Common use | Before buying |
|---|---|---|---|
| 16x20x1 | Slightly under listed size | Return grille or furnace slot | Check thickness and airflow arrow |
| 16x25x1 | Slightly under listed size | Very common residential size | Do not replace with 4-inch unless slot allows |
| 20x20x1 | Slightly under listed size | Ceiling/wall return | Confirm orientation |
| 20x25x4 | Actual depth may vary by brand | Deeper media cabinet | Match cabinet/manual |
Compatibility Warning
Do not upgrade filter thickness or MERV rating blindly. Check the equipment manual or ask an HVAC professional if you are unsure whether the system can handle it.
Related guides: Furnace Filter Sizes Chart, AC Filter Size Chart, How To Measure Air Filter Size, 16x25x1 Air Filter Size, 20x25x1 Air Filter Size, and 20x25x4 Air Filter Size.
Air Filter Size FAQs
Is the printed air filter size exact?
No. The printed size is usually the nominal retail size. The actual cardboard frame is often slightly smaller so it can slide into the slot.
Can I use a 4-inch filter instead of a 1-inch filter?
Only if the filter cabinet or slot is designed for that depth. A 4-inch filter is not a simple drop-in upgrade for a 1-inch slot.
What should I measure if the old filter is missing?
Measure the filter slot length, width and depth, then compare with common nominal sizes. Do not force a filter that bows or blocks the door.