36" x 28" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 14" Diameter + Product Details Size –

+ Product Details Size – 20"w X 10"h is the size for the duct opening measurement only

+ Product Details Size – 30"w X 26"h is the size for the duct opening measurement only

+ Product Details Perfect Fit & Easy Sizing - Designed for a 18" x 8" OR 8" X 18" duct opening (measured at the opening)

Actual Filter Size – 27 3/4"w x 15 3/4" x 1"

+ Product Details Size - 26"w X 6"h is the size for the duct opening measurement only

36" x 28" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 14" Diameter + Product Details Size –+ Product Details Perfect Fit & Easy Sizing Designed for a 36" x 28" OR 28" x 36" duct opening (measured at the opening), with actual outer dimensions of 38. 5" W x 30. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 35. 75" x 27. 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