16x25x1 vs 16x25x4 Furnace Filter: Same Size? Can You Swap Them?
Quick answer
They have the same 16 × 25 face but different depths: about ¾–⅞ inch for a "1-inch" and about 3⅝–3¾ inches for a typical "4-inch." Buy the depth your slot was built for. [S1] [S2]
- A 16x25x4 won't fit a slot built only for a 1-inch filter. Filterbuy says you can't stack 1-inch filters to fill a 4-inch slot. [S2]
- If your slot takes either size, the Department of Energy's Building America guide recommends the thickest one it fits. Deeper pleats mean more surface area and better airflow for longer. [S3]
- "16x25" is the nominal size. Actual dimensions are a little smaller and vary by brand, so compare actual sizes when you switch brands. [S1] [S3]
Actual dimensions by brand
Nominal is the size printed on the box, and actual is what the filter really measures. Figures are from Filterbuy's published tables. Filterbuy says competitor figures came from those brands' retail listings in August 2026. [S1] [S2]
| Filter (nominal) | Brand / version | Actual size (in) | Source |
|---|---|---|---|
| 16x25x1 | Filterbuy | 15.50 × 24.50 × 0.75 | [S1] |
| 16x25x1 | Filtrete (3M) | 15.68 × 24.68 × 0.81 | [S1] |
| 16x25x1 | Glasfloss | 15.50 × 24.50 × 0.875 | [S1] |
| 16x25x4 | Filterbuy | 15.5 × 24.5 × 3.63 | [S2] |
| 16x25x4 | Filtrete SlimFit | 15.5 × 24.5 × 3.75 | [S2] |
| 16x25x4 | Filtrete Deep Pleat | 15.88 × 24.56 × 4.31 (measure first) | [S2] |
| 16x25x4 | Air-Care Washable | 15.625 × 24.625 × 3.75 (measure first) | [S2] |
Filterbuy runs an affiliate program we may join. We used its tables because it publishes other brands' sizes next to its own, and we'll cross-check them against each brand's own pages.
1-inch vs 4-inch: what changes
| 16x25x1 | 16x25x4 | |
|---|---|---|
| Face size | 16 × 25 nominal | 16 × 25 nominal (same) |
| Typical actual depth | 0.75–0.875 in [S1] | 3.63–3.75 in for common brands [S2] |
| Fits a 1-inch-only slot | Yes | No |
| Fits a 4-inch slot | Only if the slot is built to take both. PNNL shows one that is [S3]. Otherwise no, and you can't stack 1-inch filters [S2] | Yes |
| Pleat depth and surface area | Shallow | Deeper pleats, more surface area, better airflow for longer [S3] |
| Replacement interval | Follow the filter maker's guidance; DOE's guide says every 3–6 months in general [S3] | Same rule. Filterbuy says its 4-inch lasts about 3× as long as its 1-inch [S2] |
Watch out: "16x25" media cabinets that aren't 4-inch
Some boxed media-filter cabinets look like 4-inch slots but take a 5-inch filter. Filterbuy lists these examples. Check the model sticker on your cabinet. [S2]
Certified alternatives
Furnace filters don't have an NSF-style certification database. The rating to compare is MERV, which comes from an ASHRAE test method. [S4] EPA suggests at least MERV 13, or the highest rating your system fan and filter slot can handle, and says to ask an HVAC technician if you're unsure. [S4] The DOE guide also says to check with your HVAC company before jumping to MERV 13 or higher. [S3]
How to tell which one you need
- Read the old filter's frame. The nominal size is printed on it. If the old filter fit correctly, buy the same size. [S3]
- No label? Measure the slot. A properly sized filter covers the duct opening and lies flush, never at an angle. [S3]
- Look for a 4-inch slot behind a 1-inch filter. Some slots take either size, and DOE's guide suggests moving up to the 4-inch if yours does. [S3]
- Check boxed cabinets for a model sticker. Filterbuy says Honeywell FC100A or Carrier/Bryant ExP codes usually mean a 5-inch filter, not a 16x25x4. [S2]
If the filter is loose
DOE's guide suggests adding adhesive weatherstripping foam around the frame of a loose filter so air doesn't slip around it. [S3] Close the slot cover afterward, but don't tape or caulk it shut, because you'll be opening it again at the next change. [S3]
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 put a 16x25x1 filter in a 16x25x4 slot?
Only if your slot is built to take both sizes. PNNL's DOE guide shows one that is. [S3] Otherwise Filterbuy says they aren't interchangeable, and you can't stack 1-inch filters to make up the depth. [S2]
Is a 16x25x4 better than a 16x25x1?
If your slot fits it, generally yes. The DOE Building America guide recommends the thickest filter the slot can take, because deeper pleats give more surface area and better airflow for longer. [S3]
Why does my 16x25x1 filter measure 15.5 x 24.5?
16x25x1 is the nominal size. Filterbuy's 16x25x1 actually measures 15.50 × 24.50 × 0.75 inches, and Filtrete's 15.68 × 24.68 × 0.81. [S1]
What MERV rating should I buy?
EPA recommends at least MERV 13, or as high as your system fan and filter slot can handle. Ask an HVAC technician if you're unsure. [S4]
Which way does the arrow go?
Point the airflow arrow into the duct, toward the furnace. [S3]
What we could not verify
- Filtrete, Glasfloss and Air-Care dimensions come from Filterbuy's comparison tables, not from those brands' own pages. We'll cross-check them in a later update.
- Filterbuy's "about 3× as long" claim for 4-inch filters is the company's own statement, not an independent test.
- Prices. They change often, so we don't list them.
Sources
- [S1] 16x25x1 Air Filters — Filterbuy. Accessed 2026-10-24. Used for: Filterbuy actual size and Filterbuy's brand comparison table for 16x25x1.
- [S2] 16x25x4 Air Filters — Filterbuy. Accessed 2026-10-24. Used for: Filterbuy actual size, brand comparison, 5-inch cabinet examples, no stacking.
- [S3] 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: Measure/fit guidance, thickest filter the slot accepts, MERV caution, arrows, 3–6 month replacement.
- [S4] What is a MERV rating? — U.S. EPA. Accessed 2026-10-24. Used for: MERV definition and MERV 13 recommendation.
Last checked 2026-10-24. Spot an error? Tell us and we'll recheck it against the source.