18" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 14" Diameter + Product Details Size – Suitable for all AC 8in diameter 12125SDCLNGBX

+ Product Details Size – 36"w X 20"h is the size for the duct opening measurement only

Actual Filter Size – 19 3/4"w x 15 3/4" x 1"

+ Product Details Perfect Fit & Easy Sizing - Designed for a 34" x 20" Or 20" x 34" duct opening (measured at the opening)

+ Product Details Size – 12" X 2" is the size for the duct opening (floor/vent hole) measurement only

18" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 14" Diameter + Product Details Size – Suitable for all AC 8in diameter 12125SDCLNGBX + Product Details Size – 36"w X 20"h is the size for the duct opening measurement only Actual Filter Size – 19 3 4"w x 15 3 4" x 1"