Common air filter sizes

Here are common nominal sizes for 1-inch furnace and AC filters. Click any size to open it in the lookup.

How to use this list

Find the size printed on your current filter's frame, then click it below to see the typical actual dimensions and filtration options. If you don't know your size yet, start with how to find your air filter size.

The first two numbers are length and width in inches, and the order doesn't matter (a 20x25 is the same as a 25x20). The last number is depth. This table covers 1-inch filters, the most common thickness for home systems. Many of these sizes also come in 2-inch and 4-inch depths. Always match the depth your slot was built for.

Common 1-inch sizes

"Typical actual size" assumes the frame is about 1/2 inch smaller in length and width and about 3/4 inch thick, a common pattern. Exact dimensions vary by brand, and some are only about 1/4 inch smaller. Check the product listing before you buy if your slot is a tight fit.

What if my size isn't listed?

This table isn't every size that exists. Filters come in many other standard sizes, and some homes need custom sizes. You can type any size into the lookup. If your measurements don't match a standard nominal size, read nominal vs. actual filter size to see how to round correctly. If standard sizes leave gaps, you may need a custom or exact-size filter.

Tips before you buy

• Double-check depth. A 16x25x1 and a 16x25x4 are not interchangeable.
• Check for multiple filters. Some homes have several return grilles, each with its own filter, and they may be different sizes.
• Pick a MERV rating that suits your home and your system. See MERV 8 vs. 11 vs. 13.
• Plan your next change. See how often to change your air filter.

This guide is general information, not professional HVAC advice. Your equipment manual and filter packaging take priority. Some links on this site may be affiliate links. See our affiliate disclosure.