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The Size Of Your Air Filter "Actual 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".

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

Second: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".

Third:So 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.

Nominal Size
Actual Dimensions
Example A
20 x 20 x 1
19 1/2 x 19 1/2 x 3/4
Example B
16 x 25 x 1
15 1/2 x 24 1/2 x 3/4
That's it! You now know the difference between "Actual Size and Nominal Size".

Want to know more?Learn what a MERV Rating is.

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