Position the edge of a framing square in the wall corner where the toilet will be installed.
When you install a new bathroom, you will need to properly frame the toilet with the wall behind it and the walls on the side. The minimum distance from the toilet to the side wall is set by local building codes. Determine the distance from the rear wall behind the toilet to the toilet's drainpipe by following the toilet's rough-in requirements. Frame the toilet to the wall correctly, during the planning stages, to avoid the hassle of the toilet not fitting into the space during installation.
Measure 15 inches from the finished side wall along the rear wall. Be sure to measure from the finished wall, not the baseboard. Mark this spot on the wall with a pencil. This is the minimum amount of clear floor space that must exist between the toilet's center line and the side wall.
Position one edge of the framing square against the finished rear wall and measure 12 inches from the finished rear wall out across the floor. This is the standard rough-in measurement for a toilet. Measure 10 inches or 14 inches if the toilet's rough-in matches either of these measurements.
Mark the rough-in measurement on the floor with a pencil. This marks the exact center point for the toilet's drain line.