All vent covers are listed by filter size. (Standard filter size is 1 inch thick, if you have thicker than a 1 inch filter please note at checkout.) The rough opening of the hole, stud to stud, should be 1/2 inch bigger than the filter you use. (Ex: 16 x 36 x 1 filter = 16 1/2 x 36 1/2 rough opening of hole.) If the current vent cover touches anything around it please note at checkout. (The total outside dimensions of a Fancy Vent will be approximately 3 inches bigger than the filter size, ex: 16 x 36 x 1 filter = 19 x 39 outside dimensions.)