Rough-In Toilet Measurements: How To Check The Specs

Last Updated on January 14, 2021 by Lynda Stevens


Measuring a toilet can be a simple process, but there are numerous parts that need to be checked to get an accurate idea of just how much space the toilet takes up. It’s also important to know the height and size of the toilet since, during replacement, you want to get a commode that actually fits in the bathroom and lines up with the plumbing.

One of the most important measurements for homeowners is the rough-in. Although it has a weird name, the rough-in is crucial. This measurement is the distance between the wall and the central floor drain or waste outlet to which the toilet is connected. Here’s how to check the specs to make sure your new toilet is one that fits your system.

What Tools Do You Need?

Picture of a measuring tape

Because toilets possess a strange shape, you need to use a measuring tool that is flexible and able to move around. The best implement to check the rough-in is a simple, loose measuring tape. These tapes are inexpensive, typically costing between $1 and $5. It’s also a good idea to have a pad of paper and something to write with solely so you don’t forget the measurement when you’re out shopping. Otherwise, you should be all set. Just make sure you can read the tape measure easily and it uses the standard units of measurement in your country for buying toilets and other appliances. For the United States, you need inches.

Why Is the Rough-In Important?


Toilet rough in dimension

The rough-in is an important part of the toilet because it lets you know where to install a new model. Manufacturers do not make many standardized toilet models, so it’s common for one model to be too big or too small for a home. While there is a general basis for how big each toilet is – usually a range of six inches – purchasing a toilet with a rough-in that is even one inch off means you won’t be able to install the new commode and will be missing out on the luxury of using the bathroom. Nobody wants to be in that situation, especially since buying the wrong toilet means costly returns and wasted time.

How to Measure the Rough-In On a Standard Toilet

Measurement picture in toilet

When you do decide to measure the rough-in, you need to know the proper place to put the tape measure. Many people make the mistake of putting the first end of the tape measure up against the wall’s mold or baseboard, which is wrong. You see, most of the wall does not have a border, and including the baseboard adds extra centimeters that shouldn’t be in the measurement and can actually mess up important specifications. So, you should be certain to place one end of the tape measure directly against the plaster or wallpaper of the wall.[1]

If you’ve done so and keep getting a weird number that is not an exact inch or even close to one, tap against the wall. If it sounds slightly hollow, you might have paneling over the drywall that is affecting the measurement. Unfortunately, it can be hard to find an exact rough-in number if you don’t know how thick the paneling is, so you will have to estimate based on the closet full inch. Always round up in this scenario rather than down.

Next, be sure to keep the tape measure even and pull the other side until it aligns with the central bolts holding the base of the toilet in place. Beneath those bolts is the central floor drain or waste outlet through which waste flows. Remember that the tape measure needs to be even to get an accurate measurement, and then read the number.

The average length of a rough-in can be either 10, 12, or 14 in. Twelve inches is the most standard, but it’s not unusual for there to be bigger or smaller toilets.

How to Measure the Rough-In On a Corner Toilet

Sometimes people install toilets so the back faces a corner instead of being flush against a wall. When this happens, it complicates the measuring of the rough-in. To get an accurate measurement, place the tape measure against one wall – again ignoring any baseboard – and measure to the central bolts. Then, repeat the process for the other wall that the toilet sits against. These two measurements should produce the same number, which is the rough-in.

How to Measure the Rough-In On a Rear Outlet Toilet

In a rear outlet toilet, the central drain through which waste flows is on the back of the toilet, and the piping runs through the wall. To get this measurement, measure from the flat wall to the center of the rear waste outlet once more. This number will be smaller than the result on a regular toilet, usually by half. So, it’s not uncommon to get measurements of 5, 6, or 7 in.


Homeowners can be flexible about the height and width of their toilet tank and bowl, but the rough-in is a feature you don’t want to get wrong when seeking a replacement. Without an accurate rough-in, the plumbing won’t connect properly and waste can’t be disposed of. Nobody wants a useless bucket instead of a functioning toilet, the jewel of modern plumbing.

To make sure you have the right rough-in toilet measurements, check your specs several times before declaring yourself done. Almost all rough-in measurements will be an even, rounded inch between 10 and 14 in. If you have a number that is wildly different, check again. Once you have the measurement, you can go on to finding the right new toilet for you!

What’s Next?

See, that wasn’t too rough! Once you have the rough-in, it only takes a few more steps to get that brand-new, potentially high tech toilet you’ve always wanted. For more information on the different types of toilets on the market, check out this link. We provide information on just about every home subject imaginable.

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