Truaire C154R 12X12(Duct Opening Measurements) Heavy Duty Floor Return Air Grille 12-Inch by 12-Inch Floor Return Air Grille, Brown Extremely ridged construction Model Size Indicates Duct Opening Measurements not Wall Opening Measurements. Over 75% free area High quality powder coated The actual face size is 13.8-inch in width and 13.8-inch in height.