36" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 38 5/8" X 20 5/8"] 8in diameter + Product Details Size - 4 X 12 Is CRFG2028 Width_14in

+ Product Details Size - 18"w X 34"h is the size for the duct opening measurement only

actual front end outer dimensions are approximately 27 5/8" width X 30 5/8" height

+ Product Details Size – 36"w X 14"h is the size for the duct opening measurement only

Actual Filter Size – 29 3/4"w x 5 3/4" x 1"

Actual Filter Size – 9 3/4"w x 35 3/4" x 1"

36" X 18" Steel Return Air Filter Grille for 1" Filter Removable Frame [Outer Dimensions: 38 5 8" X 20 5 8"] 8in diameter + Product Details Size 4 X 12 Is CRFG2028 Width_14in + Product Details Size 18"w X 34"h is the size for the duct opening measurement only actual front end outer dimensions are approximately 27 5 8" width X 30 5 8" height