16x20x1 vs 16x20x4 Furnace Filter: Actual Sizes and Which One Fits
Quick answer
Both have a 16 × 20 face, but a 16x20x1 is about ¾ inch deep and a 16x20x4 is about 3⅝ to 4⅓ inches depending on the brand. Buy the depth your slot or cabinet was built for. [S1] [S2]
- Filterbuy: 16x20x1 = 15.5 × 19.5 × 0.75 in; 16x20x4 = 15.5 × 19.5 × 3.63 in. [S1] [S2]
- Filtrete's 16x20x4 is 15.88 × 19.88 × 4.31 in, per Filterbuy, so the two brands' "4-inch" filters differ by about ⅔ inch in depth. [S2]
- Honeywell's 16 × 20 media filter (FC100A1003 / FC200E1003) is 16 × 19¾ × 4⅜ in, deeper than either. [S3]
Actual sizes by brand
Filtrete rows come from Filterbuy's comparison tables. Filterbuy says they're as published by those manufacturers and their retailers. [S1] [S2]
| Filter | Actual size (in) | Source |
|---|---|---|
| Filterbuy 16x20x1 | 15.5 × 19.5 × 0.75 | [S1] |
| Filtrete 16x20x1 MERV 8 | 15.688 × 19.688 × 0.78 | per Filterbuy [S1] |
| Filtrete 16x20x1 MERV 11 | 15.68 × 19.68 × 0.81 | per Filterbuy [S1] |
| Filterbuy 16x20x4 | 15.5 × 19.5 × 3.63 | [S2] |
| Filtrete 16x20x4 | 15.88 × 19.88 × 4.31 | per Filterbuy [S2] |
| Honeywell FC100A1003 (MERV 11) / FC200E1003 (MERV 13) | 16 × 19¾ × 4⅜ | Honeywell [S3] |
1-inch vs 4-inch at a glance
| 16x20x1 | 16x20x4 | |
|---|---|---|
| Where it goes | Return grille or thin furnace slot | A 4-inch slot or media cabinet [S2] |
| Swap into the other slot? | Only if your slot is built for both depths (DOE shows one) [S4] | Won't fit a 1-inch-only slot; Filterbuy says upgrading means a new cabinet installed by a technician [S2] |
| Change interval | Lennox: every 3 months for standard 1-inch [S5] | Filterbuy says 6–9 months for its 16x20x4 (its own claim) [S2]; Honeywell says every 6 months for its media filter [S3] |
Why depth matters more than the label
Deeper pleats give a filter more surface area, so it keeps air moving well for longer before it needs replacing. That's why DOE recommends the thickest filter your slot can hold. [S4] The catch is that "4-inch" filters from different brands aren't the same depth (see the table above), so check the seal at the edges after you switch brands. [S2]
If a filter is loose in its slot, DOE suggests adding adhesive foam weatherstripping around the frame so air doesn't slip around it. [S4]
Where to buy
We don't link to specific sellers here yet. Search for the exact part number or size on this page at a retailer you trust, compare the listed actual dimensions, and check the current price. We don't list prices because they change daily.
FAQ
Can I use a 16x20x1 in a 16x20x4 slot?
Only if the slot is built to take both depths. DOE's Building America guide shows a slot that takes either a 1-inch or a 4-inch filter and recommends the 4-inch. [S4] Otherwise, use the depth the slot was built for.
Will a Filterbuy 16x20x4 fit where my Filtrete 16x20x4 was?
Check the fit. Filterbuy says its filter is 3.63 inches deep against Filtrete's 4.31, so it sits about two-thirds of an inch shallow in a cabinet built for the Filtrete. The rails have to hold it square, so look for gaps at the edges. [S2]
What size is a Honeywell 16x20 media filter?
Honeywell lists the FC100A1003 (MERV 11) and FC200E1003 (MERV 13) at 16 × 19¾ × 4⅜ inches, for its F100/F200 16 × 20 media air cleaners. [S3]
Is 16x20x1 the same as 20x16x1?
Yes. Filterbuy says manufacturers list length and width in either order. [S1]
What MERV rating should I use?
EPA recommends at least MERV 13, or as high as your system fan and filter slot can handle. [S6]
What we could not verify
- Filtrete dimensions come from Filterbuy's tables, not 3M's own listings.
- Filterbuy's 6–9-month life for its 4-inch filter is the company's own claim.
Sources
- [S1] 16x20x1 Air Filters — Filterbuy. Accessed 2026-10-24. Used for: Filterbuy and Filtrete 16x20x1 sizes; length/width order.
- [S2] 16x20x4 Air Filters — Filterbuy. Accessed 2026-10-24. Used for: Filterbuy and Filtrete 16x20x4 sizes; cabinet fit notes; service-life claim.
- [S3] Honeywell Media Air Cleaners Professional Installation Guide (68-0239EF-12, Rev. 10-17) — Honeywell International (PDF hosted by Build.com). Accessed 2026-10-24. Used for: FC100A1003/FC200E1003 size; 6-month replacement.
- [S4] Replace Air Filter Located in Furnace or Central Heat Pump Air Filter Slot — Building America Solution Center (PNNL, U.S. Department of Energy). Accessed 2026-10-24. Used for: Slots that take 1- or 4-inch filters; thickest filter that fits.
- [S5] Air Filters — Lennox Residential. Accessed 2026-10-24. Used for: 1-inch filters every three months.
- [S6] What is a MERV rating? — U.S. EPA. Accessed 2026-10-24. Used for: MERV 13 recommendation.
Last checked 2026-10-24. Spot an error? Tell us and we'll recheck it against the source.