10" x 36" or 36" x 10" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 12.5" X 38.5"] Compatible with Duct 6" + Product Details Size -

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

actual front end outer dimensions are approximately 26 5/8" width X 12 5/8" height

+ Product Details Size – 24" x 28" or 28" x 24" is the size for the duct opening measurement only

+ Product Details Size – 34"w X 10"h is the size for the duct opening measurement only

Total outer size of this grille is

10" x 36" or 36" x 10" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 12.5" X 38.5"] Compatible with Duct 6" + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 10" x 36" or 36" x 10" duct opening (measured at the opening), with actual outer dimensions of 12. 5" W x 38. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 9. 75" x 35. 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