18"W X 18"H [Duct Opening] ALUMINUM RETURN GRILLE - EASY AIR FLOW - LINEAR BAR GRILLES [OUTER DIMENSIONS: 19.875"W X 19.875"H] Compatible With Duct 10in Think of the diameter as

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

ensuring a perfect fit

actual front end outer dimensions are approximately 18 5/8" width X 20 5/8" height

Actual Filter Size – 13 3/4"w x 19 3/4" x 1"

18"W X 18"H [Duct Opening] ALUMINUM RETURN GRILLE - EASY AIR FLOW - LINEAR BAR GRILLES [OUTER DIMENSIONS: 19.875"W X 19.875"H] Compatible With Duct 10in Think of the diameter as+ Product Details Size 18"w X 18"h is the size for the duct opening measurement only, actual front end outer dimensions are approximately 19. 875" width X 19. 875" height. High Quality High quality aluminum with counter sunk screw holes (screws included) and no sharp edges. Design Unrestricted airflow For Your HVAC system noise free components no vibrating louvers etc. Powder Coat Finish Smooth, shiny, scratch resistant, beautiful. Looks like it was