8" x 26" or 26" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 10.5" X 28.5"] Adjustable Return + Product Details Size -

+ Product Details Size - 36"w X 10"h is the size for the duct opening measurement only

Actual Filter Size – 17 3/4"w x 33 3/4" x 1"

75" width X 21

By means of the smooth surface

Actual Filter Size – 27 3/4"w x 33 3/4" x 1"

8" x 26" or 26" x 8" Cube Core Eggcrate Return Air Filter Grille for 1" Filter - Aluminum - White [Outer Dimensions: 10.5" X 28.5"] Adjustable Return + Product Details Size -+ Product Details Perfect Fit & Easy Sizing Designed for a 8" x 26" or 26" x 8" duct opening (measured at the opening), with actual outer dimensions of 10. 5" W x 28. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 7. 75" x 25. 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