Replacing a toilet is a necessary part of home repair that comes about infrequently for most homeowners. Measuring your toilet rough-in will help you pick the right replacement fixture the first time. The rough-in is the distance from the centre of the floor drain to the wall behind the toilet's tank. When measuring a rough-in where a toilet is already installed, measure from the floor bolts instead. These anchors are usually positioned alongside the centre of the floor flange.
Place one end of the tape measure against the wall at the rear of the toilet. If there is any moulding, measure from the wall itself, rather than the outside of the moulding.
Stretch the tape measure until it meets the floor bolt caps. These bolts mark the centre part of the drain.
Record the measurement from the back wall to the floor bolts. This measurement is your rough-in.
The average toilet rough-in is 12 inches, and most toilets found in retail stores match this measurement. If you have a less common 10- or 14-inch rough-in, consult with your retailer to find out what replacement options are available.