How to Identify the Size of Your Air Filter Without a Filter

Learn how to identify your AC filter size without a filter by measuring it with a ruler or inspecting your unit for an indicated size.

How to Identify the Size of Your Air Filter Without a Filter

If the size of your air filter isn't clearly labeled, you can easily measure it with a ruler. Most disposable air filters are discounted between ¼ and ½, so you should be able to use the closest standard size. To identify the size of your AC filter, remove the existing filter from its slot and examine the filter frame. The size is usually printed along the edge of the filter frame, but note that this is the nominal size of the filter, which is likely to differ from its actual size.

If the actual dimensions do not appear on the filter frame, we recommend measuring it for double checking. To measure your air filter, use a measuring tape to determine the width, height, and depth. 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. Most air filters are located on the right or bottom of the unit and can be easily removed from the slot. We recommend removing the existing filter and measuring it to confirm the actual dimensions. If an air filter is too small, this will create air gaps and contaminants will avoid filter material.

Once you know the size of your old air filter, you can easily buy a new one with the same dimensions. The dimensions indicated on the side of the air cleaner frames and printed larger on the air cleaner package are usually the nominal size dimensions. HVAC service companies typically offer air filter replacement services, as well as system repair and unit installation services. When buying an air filter, it's important to keep in mind that most filters measure a little smaller than their slot or frame, so they can easily slide into place without bending or breaking. Do not stack several smaller air filters on top of each other to place them in a larger air handler. Colorfil filters, originally created for NASA, help eliminate chemicals and odors at a molecular level that normal air filters can't.

The MERV air filter rating is a measure of its effectiveness in removing particles from the air.