How to Measure Your Air Filter:
Finding the correct size filter for your HVAC unit is essential to properly capture airborne contaminants and keeping your system running smoothly. Using a filter that is too large or too small could result in air flowing around the filter (air bypass), resulting in unfiltered air recirculating into your home or office.
If your HVAC system already has a filter being used check the filter for any printed sizing information. Most filters come labeled with two L X W X D sizes printed on the frame. Usually, there is a ‘nominal’ size that is printed in a large font and an ‘actual’ size printed in a smaller font on the frame. If your filter doesn’t have a size printed on it or if you don’t have a filter to reference you can follow the simple steps below to measure your existing air filter or air intake (where the filter is placed when in use).
Actual Size vs. Nominal Size
Actual Size- is the exact dimensions of your filter, often shown in precise fractions and is usually 1/2” – 3/4” less than the nominal size. This is also described as the filter’s “undercut”.
Nominal Size- is the actual size rounded up or down to the nearest whole or half number. The nominal size is what you typically use when shopping for a replacement filter.
Step 1
use a measuring tape to measure the length (l) & width (w). the smaller size of the two is the length of the filter. round your measurements to the nearest whole or half number.
length: 19-1/2" → 20"
width: 23-1/2" → 24"
Step 2
Measure the depth (D). this is also known as the thickness of the filter. round your measurements to the nearest whole number.
depth: 3/4 → 1"
Step 3
Put the measurements together - l x w x d
example:
Actual Size: 19-1/2" x 23-1/2" x 3/4" → nominal size: 20" x 24" x 1"
View our standard size list, which includes our nominal and actual sizes.
| Nominal Size | Actual Size |
| 1" Stock Pleated Filter Sizes | |
| 10 X 10 X 1 | 9-1/2 X 9-1/2 X 3/4 |
| 10 X 20 X 1 | 9-1/2 X 19-1/2 X 3/4 |
| 10 X 24 X 1 | 9-1/2 X 23-1/2 X 3/4 |
| 10 X 30 X 1 | 9-3/4 X 29-3/4 X 3/4 |
| 10 X 36 X 1 | 9-3/4 X 35-3/4 X 3/4 |
| 12 X 12 X 1 | 11-3/4 X 11-3/4 X 3/4 |
| 12 X 16 X 1 | 11-3/4 X 15-3/4 X 3/4 |
| 12 X 20 X 1 | 11-1/2 X 19-1/2 X 3/4 |
| 12 X 24 X 1 | 11-3/4 X 23-12 X 3/4 |
| 12 X 30 X 1 | 11-7/8 X 29-7/8 X 3/4 |
| 12 X 36 X 1 | 11-3/4 X 35-3/4 X 3/4 |
| 14 X 14 X 1 | 13-3/4 X 13-3/4 X 3/4 |
| 14 X 18 X 1 | 13-3/4 X 17-3/4 X 3/4 |
| 14 X 20 X 1 | 13-1/2 X 19-1/2 X 3/4 |
| 14 X 24 X 1 | 13-3/4 X 23-3/4 X 3/4 |
| 14 X 25 X 1 | 13-1/2 X 24-1/2 X 3/4 |
| 14 X 30 X 1 | 13-7/8 X 29-7/8 X 3/4 |
| 15 X 20 X 1 | 14-1/2 X 19-1/2 X 3/4 |
| 16 X 16 X 1 | 15-3/4 X 15-3/4 X 3/4 |
| 16 X 20 X 1 | 15-1/2 X 19-1/2 X 3/4 |
| 16 X 24 X 1 | 15-1/2 X 23-1/2 X 3/4 |
| 16 X 25 X 1 | 15-1/2 X 24-1/2 X 3/4 |
| 16 X 30 X 1 | 15-5/8 X 29-5/8 X 3/4 |
| 16 X 36 X 1 | 15-3/4 X 35-3/4 X 3/4 |
| 18 X 18 X 1 | 17-3/4 X 17-3/4 X 3/4 |
| 18 X 20 X 1 | 17-1/2 X 19-1/2 X 3/4 |
| 18 X 24 X 1 | 17-1/2 X 23-1/2 X 3/4 |
| 18 X 25 X 1 | 17-1/2 X 24-1/2 X 3/4 |
| 18 X 30 X 1 | 17-3/4 X 29-3/4 X 3/4 |
| 18 X 36 X 1 | 17-3/4 X 35-3/4 X 3/4 |
| 20 X 20 X 1 | 19-1/2 X 19-1/2 X 3/4 |
| 20 X 24 X 1 | 19-1/2 X 23-1/2 X 3/4 |
| 20 X 25 X 1 | 19-1/2 X 24-1/2 X 3/4 |
| 20 X 30 X 1 | 19-3/4 X 29-3/4 X 3/4 |
| 20 X 36 X 1 | 19-3/4 X 35-3/4 X 3/4 |
| 22 X 22 X 1 | 21-3/4 X 21-3/4 X 3/4 |
| 22 X 24 x 1 | 21-3/4 X 23-3/4 X 3/4 |
| 24 X 24 X 1 | 23-1/2 X 23-1/2 X 3/4 |
| 24 X 36 X 1 | 23-3/4 X 35-3/4 X 3/4 |
| 25 X 25 X 1 | 24-1/2 X 24-1/2 X 3/4 |
| 25 X 32 X 1 | 24-3/4 X 31-3/4 X 3/4 |
| 2" Stock Pleated Filter Sizes | |
| 12 X 12 X 2 | 11-3/4 X 11-3/4 X 1-3/4 |
| 12 X 20 X 2 | 11-1/2 X 19-1/2 X 1-3/4 |
| 12 X 24 X 2 | 11-3/8 X 23-3/8 X 1-3/4 |
| 14 X 20 X 2 | 13-1/2 X 19-1/2 X 1-3/4 |
| 14 X 25 X 2 | 13-1/2 X 24-1/2 X 1-3/4 |
| 15 X 20 X 2 | 14-1/2 X 19-1/2 X 1-3/4 |
| 16 X 16 X 2 | 15-3/4 X 15-3/4 X 1-3/4 |
| 16 X 20 X 2 | 15-1/2 X 19-1/2 X 1-3/4 |
| 16 X 24 X 2 | 15-3/8 X 23-3/8 X 1-3/4 |
| 16 X 25 X 2 | 15-1/2 X 24-1/2 X 1-3/4 |
| 18 X 18 X 2 | 17-3/4 X 17-3/4 X 1-3/4 |
| 18 X 24 X 2 | 17-3/8 X 23-3/8 X 1-3/4 |
| 20 X 20 X 2 | 19-1/2 X 19-1/2 X 1-3/4 |
| 20 X 24 X 2 | 19-3/8 X 23-3/8 X 1-3/4 |
| 20 X 25 X 2 | 19-1/2 X 24-1/2 X 1-3/4 |
| 20 X 30 X 2 | 19-3/4 X 29-3/4 X 1-3/4 |
| 24 X 24 X 2 | 23-3/8 X 23-3/8 X 1-3/4 |
| 25 X 25 X 2 | 24-1/2 X 24-1/2 X 1-3/4 |
| 4" Stock Pleated Filter Sizes | |
| 12 X 24 X 4 | 11-3/8 X 23-3/8 X 3-3/4 |
| 16 X 20 X 4 | 15-1/2 X 19-1/2 X 3-3/4 |
| 16 X 25 X 4 | 15-1/2 X 24-1/2 X 3-3/4 |
| 18 X 24 X 4 | 17-3/8 X 23-3/8 X 3-3/4 |
| 20 X 20 X 4 | 19-1/2 X 19-1/2 X 3-3/4 |
| 20 X 24 X 4 | 19-3/8 X 23-3/8 X 3-3/4 |
| 20 X 25 X 4 | 19-1/2 X 24-1/2 X 3-3/4 |
| 24 X 24 X 4 | 23-3/8 X 23-3/8 X 3-3/4 |
Don’t see your size? No problem, you can build your custom filter here!
Customize Your Air Filter in 4 Easy Steps
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Air Filters, Inc. is committed to providing a "one-stop shop" for all of your air filtration requirements. As an air filter manufacturer, we are uniquely positioned to custom make any and all types of air filters.
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