Actual Size vs. Nominal Size

When looking to replace your air filter, there are typically two different sizes you need to understand, actual size and nominal size.

Actual Size

The Actual Size consists of the true dimensions of your filter when measuring length, width and Depth (thickness). These dimensions typically include a fraction of an inch within them. For example: 19 1/2 x 19 1/2 x 3/4.

Nominal Size

What you might not realize is that filters are not sold by their actual dimensions. Instead a rounded up number is used to label filter packages. This measurement is referred to as the "Nominal Size".

What this means for you...

A filter with actual dimensions of "19 1/2 x 19 1/2 x 3/4" will have a nominal size of "20 x 20 x 1", and that will be the measurement to look for when buying your replacement filters.

Size Type Example 1 Example 2
Nominal Size 20 x 20 x 1 16 x 25 x 1
Actual size 19 1/2 x 19 1/2 x 3/4 15 1/2 x 24 1/2 x 3/4

Now you know the difference between nominal and actual size. If you need a specific (actual) size filter, no problem - just choose "custom size" when selecting a filter and we will make sure that it's that exact size.

Ready to find filters for your home?

Get Started