When installing a toilet, or replacing an old toilet, you have to make several measurements including the most important one: the distance between the toilet and the wall. The bathroom drain is very difficult to move, so your toilet has to fit on top of this drain with plenty of space behind it for the toilet base and tank. Usually the drain is positioned at a point on the floor to provide this space but sometimes it is not.
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Toilet Measurements and Depth
Toilets have many standard measurements, including height, width and depth or length. The width is 15 inches, height is just over 18 inches and the depth is 18.9 inches. The toilet tank is typically 10 inches wide (from the front to the back) and around 26 inches wide. Since the tank is added onto the back of the toilet, it adds to the total distance between the toilet and wall. When calculating your toilet's measurement from the wall, never solely calculate based on the toilet's dimensions alone, as these do not include the tank.
Toilet Position from the Wall
While the toilet itself does not have to be positioned any set distance from the wall, enough room behind the base of the toilet for the tank is necessary. The tank needs an inch of clearance from the wall for the lid, which hangs over the edge of the tank. Tanks also mount on the back of the toilet, with most of the tank resting on the base itself. So, the tank does not add its entire width to the toilet's depth. In other words, if the toilet is 19 inches deep, and the tank 10 inches wide, chances are the total measurement from the toilet to the wall is only 24 inches.
Normally, the toilet's total distance from the wall is listed as taken as the measurement from the wall to center line of the toilet drain. A standard method of measuring, it allows the customer to select a toilet based on how well it fits the existing drain. Remember, the center line of the drain is very close to the center line of the toilet. If you are planning a new installation, make the drain center line 12 to 14 inches from the wall, thus allowing for a 20- to 24-inch deep toilet.
Measuring Existing Drains
If measuring for a replacement toilet, just measure from the back wall to the center of the toilet drain and write down the measurement. Usually, the distance is 12 inches, so a standard toilet will fit just fine in this space. Oversize toilets may not fit in this area however. If you find the distance is shorter than 12 inches, consider buying a toilet that is smaller than the standard size, has a slimmer tank or has a depth less than 18 inches. Most toilets include an overall dimensional drawing, including the total distance from the front of the toilet to the back of tank, so consult this if possible.