standard distance of water closet with tank on the wall
Standard drywall is 1/2 inch thick, so the plumber should set the toilet flange at least 15-1/2 inches from the center of the flange to the wall framing. The standard distance from the back wall is 12 inches, or 12-1/2 inches from the center of the flange to the wall framing. Minimum distance in front of the toilet to the facing wall or fixture is 21 inches.