6"w X 12"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 7.75"w x 13.75"h] Adjustable Return + Product Details Size -

+ Product Details Size - 40"w X 20"h is the size for the duct opening measurement only

+ Product Details Size - 16"w X 16"h is the size for the duct opening measurement only

5" - SEE BELOW IN DESCRIPTION How To Measure A Grille

Actual Filter Size – 21 3/4"w x 35 3/4" x 1"

+ Product Details Size - 36"w X 12"h is the size for the duct opening measurement only

6"w X 12"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 7.75"w x 13.75"h] Adjustable Return + Product Details Size -+ Product Details Size 6"w X 12"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 7. 75" Width X 13. 75" Height Weather and Pest Proof These louvers are especially designed to prevent water from entering your home, and with a built in back 1 2" mesh they also protect you from annoying rodents like mice, rats, birds, and squirrels High Quality Aluminum The premium durable aluminum will never rust and it will never wear