What Is the Length of an Average Toilet Tank?

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Toilets come in different sizes.
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Installing a toilet is a difficult task that only becomes more difficult in a small bathroom. By learning a few important dimensions, you'll find the project becomes much easier. Each and every part of the toilet has different dimensions, and the dimensions vary between brands, but a few average sizes make decent guidelines for your project.


Know the Toilet Dimensions

When you start your project, you should know the dimensions you want in your new toilet. The length of the toilet tank, from one side across to the other, is measured from the edge of the toilet tank lid in most cases, unless noted by the manufacturer. Or, if your tank does not include a lid, the dimensions indicate the length from the side wall of the tank to the sidewall of the tank and do not include the lid.


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A lid may add an additional 1 or 2 inches, depending on the thickness of the lid sidewalls and its design. For instance, if the lid fits over the sides of the tank, it adds additional length to the tank. If the lid mounts flush to the tank, it does not add length.

Installation and Tank Length

When installing a new toilet, it's imperative to understand dimensions such as the tank length and width. If you need to fit the toilet into a tight space along a wall, you have to know the tank length to fit the toilet between two items such as the cabinet and bathtub or the cabinet and wall.


If you plan on squeezing the toilet into a corner, knowing this dimension tells you how much space on the other side you have for additional items. To improve your chance of success, measure your install area and buy a tank with a shorter length.

Small Tank Lengths

Tanks come in a few different sizes, and one of them is small. Small tanks vary in size; however, one standard length is 15 1/8 inches. It is common to see these tanks on toilets with bowls and seats of a similar size.


When the toilet bowl and seat are the same width, it is easy to plan your installation because you only have to consider one measurement. You do not have to account for the seat width and tank length separately.

Larger Toilet Tanks

Large toilet tanks range in size as well but typically measure from 16 3/4 inches to 18 inches wide. The additional length adds capacity to the tank, however, the actual amount of water the tank holds depends on where the user sets the float ball.


Lowering the float ball reduces the amount of water the tanks contains for each flush. So, while tank length increases the overall maximum amount of water it will hold, it does not determine the amount of water used during a flush.



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