Furnace Filter Sizes

There are hundreds, if not thousands, of furnace filter sizes - and we got your covered! PureFilters carries 900+ different filter sizes, manufactures custom sizes.

The size of your furnace filter will largely depend on your furnace, AC, HVAC unit or other filter intake tray. The easiest way to find your furnace filter size is by finding your existing furnace filter.

Below are all of our filter size categories, organized by size:

1 Inch Furnace Filters

1 inch furnace filters are by far the most common thickness. They are used in both residential and commercial furnaces, air conditioners, duct systems and HVAC units.

Below are the 5 most common 1 inch furnace filter sizes:

16x25x1 Furnace Filter

20x20x1 Furnace Filter

20x25x1 Furnace Filter

16x20x1 Furnace Filter

14x20x1 Furnace Filter

View all 1 inch furnace filters

2 Inch Furnace Filters

2 inch furnace filters are far more common in commercial and industrial settings. However there are a few residential HVAC units/systems that have a 2 inch filter intake as well.

Below are the 5 most common 2 inch furnace filter sizes

20x20x2 Furnace Filter

16x25x2 Furnace Filter

16x20x2 Furnace Filter

20x25x2 Furnace Filter

24x24x2 Furnace Filter

View all 2 inch furnace filters

3 Inch Furnace Filters

3 inch furnace filters are very rare and are used almost exclusively in residential settings. PureFilters only carries a handful of branded OEM 3 inch furnace filters.

View all 3 inch furnace filters

4 Inch Furnace Filters

4 inch filters are found in residential, commercial and industrial environments. There are several branded OEM and PureFilters branded furnace filters.

Below are the 5 most common 4 inch furnace filter sizes:

16x25x4 Furnace Filter

20x25x4 Furnace Filter

20x20x4 Furnace Filter

16x20x4 Furnace Filter

24x24x4 Furnace Filter

View all 4 inch furnace filters

5 Inch Furnace Filters

5 inch furnace filters are almost exclusively used in residential environments. There are some rare circumstances where a commercial or industrial building uses a 5 inch furnace filter, but this is quite rare.

Below are the 3 most common 5 inch furnace filter sizes:




View all 5 inch furnace filters

6 Inch Furnace Filters

6 inch furnace filters are almost exclusively used in residential environments. There are some rare circumstances where a commercial or industrial building uses a 6 inch furnace filter, but as mentioned, it is quite rare.

Below are the 3 most common 6 inch furnace filter sizes




View all 6 inch furnace filters

Often times filter may have two measurements listed on it, one is called the "nominal size" and the other is the "actual size" or "exact size. It is important to know the difference between these two measurements, learn more by reading the Guide on Furnace Filter Sizes

The easiest way to find your filter size is to simply measure it with a measuring tape. Once you know your nominal/exact furnace filter size, find it in the list below.

These are furnace filters sizes categorized by their NOMINAL SIZE in ascending order. The thickness of your filter is the last number of the nominal size. For example, for 16x25x1 the thickness is 1 inch, and for 20x20x2 the thickness is 2 inches. 

Here is a picture of a filter being measured, thickness being the 3rd image:


Request A Custom Filters

If you can't find your furnace filter, you can always request a custom size filter. Custom size filters can take up to 15 business days to deliver, and are final sales (no refunds/exchanges) since they are made to order. Click on the link below to request a custom size.

Request custom size filter


If you need help finding your filter, give us a call at 1-888-979-4284 or email us at support@purefilters.ca. We are available Monday to Friday from 9AM to 5PM Eastern Standard Time.