16" x 20" Cube Core Eggcrate Return Air Filter Grille for 1" Filter w25h25 + Product Details Size -

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

+ Product Details Size - The listed 5" diameter refers specifically to the size of the duct opening

+ Product Details Size - 26"w X 8"h is the size for the duct opening measurement only

The total outer size of this grille is the listed size plus 2 and 5/8"

16" x 20" Cube Core Eggcrate Return Air Filter Grille for 1" Filter w25h25 + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 16" x 20" OR 20" X 16" duct opening (measured at the opening), with actual outer dimensions of 18. 5" W x 22. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 15. 75" x 19. 75" x 1" Premium Airflow Efficiency High performance cube core eggcrate design allows 95% airflow efficiency, reducing energy costs and maximizing HVAC system lifespan. Durable, Rust Free Aluminum