How Do I Measure My Air Filter?

At Air Filters Delivered, a common question we hear is "How do I know what size air filter I need?" Often the nominal size is printed on the side of the filter, but when it's not, you'll need to know how to measure an air filter. Watch the video below for step-by-step instructions to find the actual dimensions and get the nominal size for your system. Keep in mind that some HVAC systems require more than one air filter, so make sure you have the right measurements for all of them.

When you need to replace your filter, these simple steps will help you measure the right dimensions. Remember, regular maintenance of your home’s cooling and heating system is essential to ensure it operates efficiently. Proper maintenance will keep good air quality in your home, increase the life span of your system, and consume less energy lowering your bills.

Your filters should be changed every 30 to 90 days depending on the type and efficiency of your filter. However, according to Energy Star, filters should be changed every month during peak summer and winter months when your HVAC system is operating at its highest capacity.

For safety, turn off your HVAC unit before attempting to change the filter. If you can't figure out how to turn off the unit, turn off the breaker. Most air filters are located to the right or bottom of the unit and can be easily pulled out of the slot. Although not common, some filters are found in air vents instead. If that is the case, you might need to contact a professional for assistance.

How to Measure an Air Filter Video Transcript

How To Measure Your Air Filter

You Know Your TShirt Size

That’s It!

You Know Your Coffee Size

That’s It!

But What Is Your Air Filter Size?

Locate Your Air Return Vent,

Ceiling Air Return Vent,

Or Air Handler

Open Up Air Vent

Take Out Filter & Check For Size

Or Measure Each Side

19.75 inches or 20 inch (Nominal Size)


19.75 inches or 20 inch (Nominal Size)

Measure Depth

0.75 inches or 1 inch (Nominal Size)

20x20x1 (Nominal Size)

19.75x19.75x0.75 (Actual Size)


Follow these 3 easy steps to measure your HVAC filter size:

  • Step 1 - Measuring Length and Width (L x W). (If your filter is not a square, the smallest measurement goes first).

  • Step 2 - Measure the thickness (Depth) of your filter from front to back.

  • Step 3 - Put Your measurements together (L x W x D).

It’s as simple as that! You are now ready to buy the right filter for your HVAC. Wondering what to do with your old filter now that you’ve measured it? Read more to find out how to properly dispose of your air filter or if your dirty air filter is recyclable.

Most Common Air Conditioner Filter Sizes

At Air Filters Delivered, we offer more than just standard size filters. Our product assortment contains every hard-to-find size you can imagine, in addition to custom sizes depending on your specific needs. Below are lists of the most common air filter sizes by depth.

    • 1 inch: 16x25x1, 20x20x1, 20x25x1, 16x20x1, 14x18x1,14x20x1, 14x24x1, 14x25x1, 14x30x1, 18x20x1, 20x30x1, 24x24x1, 12x24x1, 14x14x1, 16x24x1, 20x24x1, 12x12x1, 12x20x1, 16x30x1, 18x18x1, 24x30x1, 10x30x1, 12x30x1, 16x16x1, 18x24x1, 18x30x1, 20x22x1, 25x25x1, 15x20x1, 20x23x1
    • 2 inch: 20x20x2, 20x25x2, 16x25x2
    • 3 inch: 16x25x3
    • 4 inch: 20x25x4, 16x25x4, 20x20x4, 16x20x4
    • 5 inch: 20x25x5, 16x25x5
    • 6 inch: 20x25x6

Know Your Filter Size?

Enter it here to quickly find a replacement

Cant find a size?
Create your own custom size filters here.