20"w X 30"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 21.75"w x 31.75"h] 10" Diameter By simply measuring the width

By simply measuring the width or the length of the vent

to Ensure Perfect Smooth Finish

+ Product Details Size - 20"w X 30"h is the size for the duct opening measurement only

+ Product Details Perfect Fit & Easy Sizing - Designed for a 20" x 12" OR 12" x 20" duct opening (measured at the opening)

20"w X 30"h Aluminum Exterior Gable Louver Vent for Walls & Crawlspace - Weather-Resistant Air Grille with Screen Mesh - [Outer Dimensions 21.75"w x 31.75"h] 10" Diameter By simply measuring the width+ Product Details Size 20"w X 30"h X 2"d (for duct opening measurement only); actual front end outer dimensions are 21. 75" Width X 31. 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