How to Accurately Measure Air Filters for Your Home

Learn how to accurately measure air filters for your home with these easy steps. Find out how to identify nominal sizes and take accurate measurements.

How to Accurately Measure Air Filters for Your Home

If you're looking to replace the air filter in your home, it's important to make sure you get the right size. To ensure that the next filter you purchase is the correct size for your system, you should measure the inside dimensions of the air cleaner inlet. The easiest way to identify the size of the AC filter is to remove the existing filter from its slot and examine the filter frame. Typically, the filter size is printed along the edge of the filter frame.

Note that the size shown in bold type on the filter frame is the nominal size of the filter, which is likely to differ from its actual size. If the actual dimensions do not appear in small print on the filter frame, we recommend measuring the filter for double checking. To measure the air filter, use a measuring tape to determine the width, height, and depth. If the filter is not a square, the smallest measurement goes first (L x W). If a pre-existing filter is not available, inspect the unit for an indicated size.

If it is easy to access, measure the slot in the air cleaner housing or refer to the oven's operating manual for more information. For air filters, the dimensions of length and width are interchangeable, although conventionally the largest of the measurements is the width and the shortest is the length. Because AIRTEVA air filters have a patented leak protection seal, the filter does not have to be adjusted from edge to edge. When in doubt, you can always measure your air filter with a ruler or any other measuring device. Building a custom air conditioner or oven filter allows you to choose specific dimensions if standard sizes don't work for you. If the return grille is in the ceiling, you may prefer to use a filter that has a slightly larger actual size, so that the filter doesn't fall on you when you open the vent. Most air filters are located on the right or bottom of the unit and can be easily removed from the slot.

There are literally thousands of sizes of air filters, and HVAC manufacturers are incentivized to make it as complicated as possible so that you get stuck paying for their overpriced replacements. Since HVAC technicians come to your home and evaluate your specific unit, they know what type of filter your oven can handle and what is best for your system. Most white pleated air filters are inherently the same within each efficiency level, and vary slightly, if at all, between brands. When buying air filters, you will see the words “nominal size” and “actual size” together. When buying an air filter, it's important to keep in mind that the air filtration industry standard is to make filters measure a little smaller than their slot or frame, so they can easily slide into place without bending or breaking. You also don't want to place an air filter 1 in a slot 2 because the air takes the path of least resistance and will flow around the filter instead of through it if it's not the right size. To ensure that you get an accurate measurement for your next air filter purchase, follow these steps:

  • Remove existing filter from its slot
  • Examine filter frame for nominal size
  • Measure inside dimensions of air cleaner inlet
  • Choose an appropriately sized replacement
By following these steps and taking accurate measurements of your existing air filters before purchasing replacements, you can ensure that your new filters fit properly and provide optimal filtration performance.

Penelope Ruelle
Penelope Ruelle

Passionate zombie lover. Proud bacon ninja. Tea ninja. Avid social media junkie. Extreme internet evangelist. General travelaholic.