How To Measure A Toilet: Our Guide To Getting The Dimensions Just Right

Despite how much they are used, the toilet is seldom thought about by the average individual. Instead, people would rather that the commode be a discrete feature of any home, kept a secret until it is needed. However, there are a few occasions when it needs to be thought of. When it breaks, if it’s clogged, if someone feels the call of nature, and if it needs to be replaced are the four most common scenarios when someone remembers the toilet. But how is it supposed to be measured for repairs or replacement?

Required Tools

Tape measure

Not all toilets are made to the same dimensions, and most are not boxes with areas that are easily calculated. This means a flexible measuring instrument is necessary to get the dimensions of the average toilet. The best is a loose tape measure. These are inexpensive and can cost as little as $2-$5. Besides the tape measure, it’s a good idea to also have a notepad and something to write with to note down measurements.

The Rough-In

Tape measure measuring the width from the wall

The first thing to measure on a toilet is the rough-in. The rough-in determines how far away the center of the base of the toilet is from the wall. To get this measurement, crouch down and place one end of the tape measure up against the wall. Then, lay the tape measure flat against the floor until it is alongside the central bolts of the toilet. These bolts will be on the base and tend to be in the center. This measurement (wall to central bolts) is the rough-in. Most toilets have a standardized measurement of either 10 in., 12 in., or 14 in. Write down this measurement and move on.

Bowl Height


Toilet chair diagram at the back

The bowl portion of the toilet is the section with the seat and lid. The bowl is the open area which fills with water and is the portion that is often cleaned. To measure the height of the bowl, place one end of the tape measure on the floor and measure to the top of the lid. Standard bowl height measurements are between 17 in. and 19 in., but don’t worry if your toilet is a little different. Make sure to record the height on your notepad.

Bowl Length

The bowl length can be taken by measuring from the toilet tank to the front of the bowl. Simply place one end of the tape measure up against the take and see how far it stretches before the bowl ends. A standard measurement for this section of the toilet is between 16 in. and 19 in.

This measurement will be affected by whether or not your toilet has a round or elongated bowl. A round bowl with being shaped like a perfect circle, similar to a typical soup or cereal bowl. An elongated one will be more oval in shape, or longer than it is wide. Elongated bowls are more comfortable, but round toilets work better in small spaces.

Gallons Per Flush

It’s important to measure how much water a toilet uses per flush because the plumbing can only handle so much liquid. If a toilet needs more than the pipes can handle, then it won’t flush properly or could cause a pipe to burst. However, if a new toilet uses even less water, it shouldn’t cause a problem.

In previous decades, a toilet could use as much as seven gallons of water per flush. However, the government started to regulate how much water toilets could be designed to use. Ever since the 1990s, most manufactured models only need to use 1.6 gallons per flush. A low flow toilet, one that uses even less water, can use as little as 1.3 gallons. To figure out how much water your commode uses per flush, look at the flat space between the bowl and the tank. Usually the number is written there as “1.6 GPF.” GPF stands for “Gallons per Flush.” If there is no marking, then you will need to do some light calculations. Follow these steps to find your number.

  1. Measure the length of the tank.
  2. Measure the width of the tank.
  3. Measure the height of the water in the tank without flushing.
  4. Measure the lowest point the water in the tank reaches when it is flushed.
  5. Subtract the number discovered from step 4 from the number in step 3.
  6. Multiply the length times the width times the number in step 5.
  7. Divide the number in step 6 by 231 to get gallons per flush.

So, what should an answer from all these calculations look like?

Let’s say the tank is 12 in. long and 8 in. wide. The water pre-flush is 6 in. and reaches 2 in. at its lowest point during a flush.

First, subtract 2 from 6, which is the equation 6-2. This equals 4.

Second, multiple the length times the width times 4. This is the equation 12 x 8 x 4, which equals 384. This number then needs to be divided by 231, which is the equation 384/231. The answer is 1.66 or 1.7. This is how many gallons per flush are used by the toilet. Remember this number because it can help you when calculating your water efficiency or when buying a replacement.


Once you know how to measure a toilet, you can use the information to help you make repairs or even buy a brand new model. Toilets aren’t something that is commonly replaced, but they go out of style quickly and manufacturers are currently working on making new models that are more energy efficient, use less water, and are far more stylish in the modern world. 

What’s Next

If you’re thinking about a replacement, follow these simple steps to help you find the toilet of your dreams. To find more how-to guides, tips, tricks, and reviews, check out our website. There’s a world of information waiting out there, and while it’s up to you to find it, we can help you locate it!  Visit this page to find out the best toilets that we recommend for your home.


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