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16x25x1
Quick answer: A 16x25x1 air filter is a nominal size; it actually measures about 15½ × 24½ × ¾ inches. It is among the most common furnace and return grille sizes in North America. Its nominal face area is about 2.78 square feet, so a single one comfortably suits roughly 800–1,000 CFM at typical 1-inch filter velocities.
Why 16x25x1 is everywhere
Many builders standardized on 16-inch-wide return openings because they fit between wall studs on 16-inch centres and align with common furnace return cabinets. The 25-inch length matches a typical furnace cabinet height cut-out or a standard return grille. The result is that 16x25x1 is one of the most widely stocked filter sizes, available in every MERV level from basic fibreglass to MERV 13, in grocery stores, hardware stores and online.
Dimensions at a glance
| Measure | Nominal | Typical actual |
|---|---|---|
| Width | 16 in | about 15½ in |
| Length | 25 in | about 24½ in |
| Depth | 1 in | about ¾ in |
| Face area | 2.78 ft² (nominal) | about 2.64 ft² (actual) |
Some brands make "exact fit" versions closer to 15¾ × 24¾ inches. If your old filter differs, match its actual size.
Where you will find it
- A horizontal or vertical slot between the return duct and a gas furnace.
- A wall return grille in a hallway, often near the thermostat in houses built since the 1970s.
- A ceiling return grille in single-storey homes, condos and townhouses.
- The filter rack of some air handlers paired with heat pumps.
If yours is in a grille, the grille's face may look larger than 16 × 25; the filter frame inside is what counts.
Airflow capacity
At 300 feet per minute — a common rating velocity for 1-inch filters — a 16x25 moves about 2.78 × 300 ≈ 833 CFM. That suits about a 2-ton system on its own. For a 3-ton system at roughly 1,200 CFM, one 16x25x1 runs at about 430 fpm, which raises resistance; two return grilles or a deeper filter can help. See airflow and pressure drop.
Choosing MERV in this size
Because 16x25x1 is so common, every efficiency level is easy to find. MERV 8 is a typical baseline. MERV 11 is widely available and suits many systems. MERV 13 in 1-inch format adds resistance, so it is best where airflow headroom has been confirmed. Compare in MERV 8 vs 11 vs 13.
Worked example
A condo owner has one ceiling return with a 16x25x1 filter and a 2-ton heat pump moving about 800 CFM. Face velocity is 800 ÷ 2.78 ≈ 288 fpm, close to the typical rating point. They currently use MERV 8 and want more dust capture. They try MERV 11, check airflow at the bedroom registers, and see no noticeable change after two weeks. They set a 60-day change interval because the ceiling grille is above a high-traffic hallway.
Illustrative note (2026-10-29): This example was prepared on 2026-10-29 for illustration. The condo, airflow and results are hypothetical; check your own system and ask an HVAC technician if airflow changes.
Upgrading to 16x25x4
If your furnace has room for a media cabinet, a 16x25x4 filter offers several times the media in the same face size. See the 16x25x4 guide and 1-inch vs 4-inch.
Buying tips for this size
- Multi-packs are common and usually cheaper per filter.
- Check the MERV, not only the marketing name.
- Confirm actual size on the listing — 15.5 × 24.5 × 0.75 is typical.
- Buy enough for a season so the next change is not delayed.
- If you use subscriptions, compare per-filter cost with store prices; see filter subscriptions.
Installing it correctly
Slide the filter in with the arrow pointing toward the furnace — or into the ceiling for a ceiling return. In a grille, close the door and check that latches catch fully. In a furnace slot, refit the cover so air cannot leak around it. A properly seated 16x25x1 should not rattle.
How often to change
Common guidance for a 1-inch pleated filter is one to three months. With pets, smoking, renovation dust or long run times, the shorter end applies. The replacement schedule offers a starting interval, but monthly visual checks are the best guide.
Yearly cost
At a hypothetical $10 per filter changed every 90 days, a 16x25x1 costs about $41 a year; at 60 days, about $61. Use the cost per year tool with your prices.
Similar sizes
Do not confuse 16x25x1 with 16x24x1, 15x25x1 or 16x25x2. They look close but leave gaps or will not fit. A 16x20x1 is five inches shorter. If unsure, measure using how to measure an air filter.
Fibreglass, pleated and washable versions
In 16x25x1 you will see three broad types. Flat fibreglass panels are inexpensive and very open, mainly protecting equipment. Pleated filters, from MERV 5 to MERV 13, capture much more fine dust and are the most common choice. Washable or permanent filters with plastic frames exist too; they avoid repeat purchases but must be cleaned and fully dried, and many have low MERV ratings. Damp media can harbour odours, so follow the maker's cleaning directions closely.
If the slot is loose
Some furnace slots are slightly oversized or have lost their cover. A loose 16x25x1 lets air leak around the edges. Foam weatherstrip on the slot cover, or a replacement cover from the furnace maker, can tighten things up; an HVAC technician can advise.
Two filters in series
Occasionally a home has a 16x25x1 at the furnace and another filter in a return grille. Two filters in a row add resistance without much benefit. Ask a technician which location the system was designed for and use only that one.
Frequently asked questions
Is 16x25x1 the same as 25x16x1?
Yes. The order of the two face dimensions does not matter.
My old filter says 15.5x24.5. Is that 16x25?
Yes. That is the typical actual size of a 16x25x1 filter.
Can I use 16x25x1 filters in a 4-inch cabinet?
No. It will leave gaps and bypass air. Use the matching depth.