Home › Furnace Filter Size Chart
Furnace Filter Size Chart
Quick answer: This chart lists common furnace and return grille filter sizes with their typical actual dimensions, face area and approximate airflow at 300 feet per minute. Find your nominal size from the old filter, confirm the actual size matches, and use the airflow column to see whether one filter suits your system. Actual sizes vary slightly by brand.
How to use this chart
Start with the nominal size printed on your old filter, or measure and round up with the filter size finder. Find that row, check that the typical actual dimensions match your old filter within about ⅛ inch, and note the face area. The airflow column multiplies nominal face area by 300 fpm, a common rating velocity for 1-inch filters, to give a rough sense of how much air one filter handles comfortably. It is a planning guide, not a system design.
One-inch sizes
| Nominal | Typical actual (in) | Face area (ft²) | ~CFM at 300 fpm |
|---|---|---|---|
| 10x20x1 | 9.5 × 19.5 × 0.75 | 1.39 | 417 |
| 12x24x1 | 11.5 × 23.5 × 0.75 | 2.00 | 600 |
| 14x20x1 | 13.5 × 19.5 × 0.75 | 1.94 | 583 |
| 14x24x1 | 13.5 × 23.5 × 0.75 | 2.33 | 700 |
| 14x25x1 | 13.5 × 24.5 × 0.75 | 2.43 | 729 |
| 15x20x1 | 14.5 × 19.5 × 0.75 | 2.08 | 625 |
| 16x20x1 | 15.5 × 19.5 × 0.75 | 2.22 | 667 |
| 16x24x1 | 15.5 × 23.5 × 0.75 | 2.67 | 800 |
| 16x25x1 | 15.5 × 24.5 × 0.75 | 2.78 | 833 |
| 18x24x1 | 17.5 × 23.5 × 0.75 | 3.00 | 900 |
| 20x20x1 | 19.5 × 19.5 × 0.75 | 2.78 | 833 |
| 20x24x1 | 19.5 × 23.5 × 0.75 | 3.33 | 1,000 |
| 20x25x1 | 19.5 × 24.5 × 0.75 | 3.47 | 1,042 |
| 20x30x1 | 19.5 × 29.5 × 0.75 | 4.17 | 1,250 |
| 24x24x1 | 23.5 × 23.5 × 0.75 | 4.00 | 1,200 |
| 25x25x1 | 24.5 × 24.5 × 0.75 | 4.34 | 1,302 |
Deep media sizes
| Nominal | Typical actual (in) | Face area (ft²) | Notes |
|---|---|---|---|
| 16x25x4 | 15.5 × 24.5 × ~3.6–3.75 | 2.78 | Depth varies by cabinet |
| 20x25x4 | 19.5 × 24.5 × ~3.6–3.75 | 3.47 | Very common media size |
| 16x25x5 | about 15.5–16 × 24.5–25 × ~4.4–4.9 | 2.78 | Brand-specific cabinets |
| 20x25x5 | about 19.5–20 × 24.5–25 × ~4.4–4.9 | 3.47 | Brand-specific cabinets |
Deep filter airflow depends heavily on media area, so we do not list a CFM figure; check the manufacturer's data. See 16x25x4 and 1-inch vs 4-inch.
Reading the airflow column
The 300 fpm figure is a common reference point, not a limit. Many systems run filters somewhat faster, which raises resistance. If your system moves more air than the column shows, you may want more return area, a deeper filter or a lower MERV in 1-inch format. A rule of thumb for airflow is roughly 350 to 400 CFM per ton of cooling; a technician can tell you your actual airflow. Use the return grille sizer to estimate needed face area.
Worked example
A homeowner's 2.5-ton system moves about 1,000 CFM through a single 16x24x1 filter. The chart shows about 800 CFM at 300 fpm, so actual face velocity is about 375 fpm. They compare with a 20x24x1 at 1,000 CFM — exactly 300 fpm — but their grille only fits 16x24, so changing size would mean replacing the grille. They decide to stay with MERV 8 in the existing size and ask a technician about return capacity at the next service.
Illustrative note (2026-10-29): This example was prepared on 2026-10-29 for illustration. The system, airflow and decision are hypothetical; the chart's actual dimensions are typical patterns, not a specific brand's specifications.
Sizes with odd fractions
Some equipment uses fractional nominal sizes such as 11¼ × 21¼, 12½ × 24 or 15¾ × 24¾. These are often furnace-specific. If your filter does not appear above, check the furnace label or order custom sizes by actual dimensions.
Orientation
Filters are listed with the smaller face dimension first by convention. A 25x16x1 is the same as a 16x25x1. Depth is always last.
Popular sizes
The most common sizes in North American homes include 16x25x1, 16x20x1, 20x20x1 and 20x25x1. Each has a full guide.
In Canada
Sizes are the same; see Canada filter sizes for metric conversions and retail notes.
Checking against your filter
- Measure your old filter's actual dimensions.
- Find the row whose typical actual size matches within about ⅛ inch.
- If two rows look close, choose the one whose nominal size matches your slot.
- If none match, it may be a custom or brand-specific size.
Why actual sizes vary
Some brands make filters a touch larger or smaller than the typical figures, and frames can swell slightly in humid storage. That is why we suggest matching within about an eighth of an inch rather than expecting an exact match.
Multiple filters in one system
Larger systems sometimes use two filters side by side in a rack, or several return grilles. Add the face areas together to estimate total capacity: two 16x25 filters give about 5.56 square feet, or roughly 1,670 CFM at 300 fpm. Change all of them at the same time so one clogged filter does not force air through the others at higher velocity. Some packaged rooftop and commercial-style units take four or more filters; their sizes are listed on the unit's access panel.
Two-inch sizes
Two-inch filters such as 16x25x2 or 20x25x2 are less common in stores but used by some air handlers. Their actual depth is typically about 1¾ inches. They offer more media than 1-inch filters at the same face size.
Printing the chart
Many homeowners print the row for their size and tape it inside the furnace closet, alongside the date of the last change and the MERV they use.
Frequently asked questions
What is the most common furnace filter size?
16x25x1 is among the most common, along with 20x25x1, 16x20x1 and 20x20x1.
Can I use a filter one inch smaller?
It will leave a gap. Use the correct nominal size.
Why do deep filters have no CFM figure?
Their capacity depends on pleat design; use the maker's data.