How Do I Know What Size Air Filter I Need?

Where do I find my size?

Air filter sizes can look a bit intimidating, especially when a great deal of homes have multiple filters of different sizes. Second Nature is here to make filter buying EASY. Once you enter your filter sizes with us just once, not only will you not have to remember when it's time to change them, but you will no longer need to remember those tricky sizes.

In order to find the size of pleated filter(s) used in your home, you need to look no further than your existing filters. On the outer frame, you will see at least one set of numbers. If you see two sets of numbers, the filter size needed to order replacements is the nominal size, not the actual size. You can ignore the actual size printed on your filter for this task, as the nominal size is the number set needed to order new filters.

Your filter size (again, referencing the nominal size for your filter here) will look something like this: 20" x 20" x 1" or 20" x 25" x 1" or 14" x 20" x 2"

The size of your pleated air filter is always presented in a string of three numbers, with the first number representing the length, the second number representing the width, and the last number representing the thickness.

If you’re still not sure what size filter(s) your home needs, feel free to reach out to us.

Alec Lower

Content Writer

Alec is a third-year member of the team at Second Nature. He brings expert knowledge of a myriad of home air filtration topics including HVAC filters, filtration efficiency, and indoor air quality.