How to measure your air filter

We know that with all the different air filter sizes, choosing the right one for you can be a bit daunting. There are literally thousands of sizes of filters in use and HVAC manufacturers are incentivized to make it as tricky as possible (so you are stuck paying for their overpriced replacements!)

Don’t worry, we’ve got you covered.

Start by checking the size written on the side of your filter

Most filters have a size written on the side of them, and that is where you want to start. Generally, there is a ‘nominal’ size written in big print, as well as the ‘actual’ size written in smaller print below or to the side. All of the filters listed on are listed by nominal size unless specifically labeled otherwise.

No size written on your filter? No problem.

If the size is not written on the side of your filter, the next step is to take out your trusty tape measure. You need to measure the length x width x depth.

Measuring filter length and width

The length and width dimensions are interchangeable, though conventionally the first number is the smaller between the two.

Determining filter depth

Standard filters are nominally 1” (actual 0.75”), 2” (actual 1.75”), and 4” (actual 3.75”) deep. If your filter is a different depth, then you need to look for your brand on our whole house replacement filters page.

Find Common Filter Sizes

Once you find your size, you can search for it on our common filter sizes page. However, if you don’t see your size, you can create it yourself using our custom filter tool.

A note on nominal vs. actual sizes. The size listed in large print on the size of your filter is generally the ‘nominal’ filter size. The actual filter size is generally .25” to .5” less. We do our best to specify actual dimensions throughout our website so that there is no confusion. However, filters within .25” or less of your existing filter are generally interchangeable.

Still confused? No problem, we’re happy to help simply call us at 855-FILTBUY or send us a note on our contact page. We answer all correspondence within 24 business hours.