16" x 12" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 6" Diameter By simply measuring the width

By simply measuring the width or the length of the vent

actual front end outer dimensions are approximately 30 5/8" width X 36 5/8" height

Installation – Easy drop ceiling installation

actual front end outer dimensions are approximately 12 5/8" width X 18 5/8" height

If your hole is 14" wide by 20" tall

16" x 12" Cube Core Eggcrate Return Air Filter Grille for 1" Filter 6" Diameter By simply measuring the width+ Product Details Perfect Fit & Easy Sizing Designed for a 16" x 12" OR 12" X 16" duct opening (measured at the opening), with actual outer dimensions of 18. 5" W x 14. 5" H. Please check the measuring guide to ensure a proper fit. Filter Size 15. 75" x 11. 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