16" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 18 5/8" X 20 5/8"] Supply Grille Conveniently taped together as a

Conveniently taped together as a single piece

Think of the diameter as a straight line from one end to the other

Actual Filter Size – 19 3/4"w x 21 3/4" x 1"

Actual Filter Size – 11 3/4"w x 19 3/4" x 1"

16" X 18" Steel Return Air Filter Grille for 1" Filter - Removable Frame - [Outer Dimensions: 18 5/8" X 20 5/8"] Supply Grille Conveniently taped together as a+ Product Details Size 16"w X 18"h is the size for the duct opening measurement only, actual front end outer dimensions are approximately 18 5 8" width X 20 5 8" height Actual Filter Size 15 3 4"w x 17 3 4" x 1" High Quality High quality solid stamped steel with counter sunk screw holes (screws included) and no sharp edges Installation Location Sidewall and ceiling Design Removable door face for easy filter change & cleaning uses a 1" thick filter.