12" [Duct Opening] Round Ceiling Diffuser - Easy Air Flow - HVAC Vent Duct Cover [White] - [Total Outer Dimensions: 16"] Color_R-8.0 Pink Think of the diameter as

Think of the diameter as a straight line from one end to the other

+ Product Details Size – 24" x 24" with 14" collar T-Bar drop ceiling perforated return grill - metal back casing

With a 6" diameter for the duct opening measurement

Actual Filter Size – 24 3/4"w x 17 3/4" x 1"

12" [Duct Opening] Round Ceiling Diffuser - Easy Air Flow - HVAC Vent Duct Cover [White] - [Total Outer Dimensions: 16"] Color_R-8.0 Pink Think of the diameter as+ Product Details Size The listed 12" diameter refers specifically to the size of the duct opening. However, please note that the total outer dimensions of the grille measure 16" in diameter. Design Heavier gauge than needed, built for durability and long life in mind, but still light and handy. (Screws included). Airflow Easy unrestricted airflow for your HVAC system. Powder Coat Finish Smooth, shiny, scratch resistant, beautiful. Looks like it was