Steps 1 & 2

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

Step 3

Measure the thickness (Depth) of your filter from front to back.

Step 4

Put Your measurements together (L x W x D).

Actual Size

A filter’s true dimensions.

Example: 19.75” x 19.75” x 1”

Nominal Size

Rounded numbers used by manufacturers.

Example 20” x 20” x 1”

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