is at least 12 inches from wall to centerline of toilet waste rough-in! If it were to the roughed in wall not couting drywall...it better to have a little more clearance than half inch thickness of drywall, seems to me...!! If you end up with less than 12 inch gap ...they do sell a toilet for a 10 inch space between centerline and wall but they cost more money and are harder to find and have less options to choose from in terms of style. good luck LJ