Truaire C170 16X08(Duct Opening Measurements) Return Air Grille 16-Inch by 8-Inch Sidewall or Ceiling Return Air Grille, White Heavy gage all steel construction Model Size Indicates Duct Opening Measurements not Wall Opening Measurements. 1/2-inch spaced fins High quality powder coated The actual face size is 17.75-inch in width and 9.75-inch in height.