The toilet is probably the most important part of your bathroom, and knowing where to rough-in the drain is critical to the proper placement of the toilet. Where you place the toilet determines how much room there is in the bathroom. Follow the placement guidelines for standard toilets to make sure that you locate the toilet properly.
Standard Drain Placement
The standard placement for a toilet drain in the bathroom is 12 inches from the wall behind the toilet. The 12-inch measurement runs from the wall itself to the dead center of the drain. When measuring to place your drain hole, first make a mark at 12 inches and then create the outline for the drain hole around this mark. Many plumbers will use the toilet flange as the template to draw the outline for the drain hole. You can also use a compass to draw the outline for the hole.
Why This Drain Placement?
The placement of the drain 12 inches from the wall allows enough room to install the toilet. The drain is always placed far enough from the wall to allow room for both the toilet and its water tank. The tank always extends back 12 inches from the center of the toilet where the drain is located. This is the measurement for nearly all standard toilets, allowing for interchangeability of one toilet for another if a toilet gets old or breaks down.
Alternative Drain Placement
Some drains are placed closer to the back wall because the toilet tank is not as deep as on a traditional toilet. If the distance from the center of the drain hole to the back of the tank is only 10 inches, it is possible to place the drain 10 inches from the wall. This is only possible on smaller toilets. Each toilet will specify the distance required from the drain hole to the wall in the documentation. It is important to check this before you begin installing a toilet.
Distance from Side Wall
The other dimension to consider in some toilet drain installations is the distance from the the wall nest to the toilet. This distance to a side wall is just as important in smaller bathrooms because ignoring proper distances can result in a very cramped space. Most toilets are only about 1 foot wide, but you will need 15 inches of space on either side to properly access the toilet. Therefore, the proper distance for a drain from a side wall is at least 15 inches. This also applies to the distance from cabinets or tubs nest to the toilet.