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Toilet Rough-In Dimensions: How to Measure a Toilet Accurately

By Mikael Short
January 13, 2022

The #1 mistake people make when purchasing a new toilet is ordering the one with the wrong toilet rough-in dimension. Without renovation or new plumbing, it may be impossible to install a toilet rough-in that doesn’t match your existing bathroom set-up.

For sanitary reasons, most toilets can’t be returned once the package has been opened, so you may end up having to purchase a new toilet on top of keeping the incorrect one!

To avoid this costly and time-consuming mistake, we’ve outlined the step-by-step process for how to measure a toilet rough-in size, no matter what toilet you own.

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What is a Toilet Rough-In?

The rough-in size of a toilet is the distance between the bare wall and the center of the toilet drainpipe, also known as the toilet flange. An accurate rough-in size ensures there will be enough space between the drainpipe and the wall for the backside of your toilet and the toilet tank of your toilet to fit when installed.

When purchasing a new toilet, measuring and knowing the correct toilet rough-in should be your number one priority.

Standard Toilet Rough-In Sizes

skirted toilet in a modern bathroom

The standard toilet rough-in is 12 inches, but don’t assume you have a 12” rough-in without measuring! Some older homes come with 10” or 14” rough-in sizes. You may also find 10” rough-in sizes in powder rooms, half baths, or other small bathrooms to save space.

The rare 14” rough-in size allows for more room between the toilet and the wall. Often, you have to special order either of these rough-in sizes when compared to the standard 12” rough-in size.

Some types of toilets, such as two-piece toilets, are flexible when it comes to rough-in size, but others are not. That’s why it’s wise to make sure you choose a toilet with a matching rough-in size to your existing bathroom or water closet.

Can I replace a 10-inch rough in with a 12-inch rough in?

Short answer: no. It’s ideal to find a toilet that matches your existing toilet rough-in dimensions so you don’t have to call a plumber to update your plumbing, which could drastically increase your toilet replacement cost.

While a 10-inch rough-in toilet can plausibly fit into a 12-inch rough-in (though a longer connector may be needed), the same cannot be said for using a 12-inch rough-in toilet in a 10-inch rough-in. A 12” rough-in toilet will not fit in a bathroom with a 10” rough-in size.

Toilet Rough-In Measurement: A Step-by-Step Guide

What’s great about the rough-in size is that you don’t need to call a plumber to find it—it’s simple enough to measure yourself!

How to measure a toilet rough in for standard toilets, corner toilets, and wall mount toilets

How to Measure a Toilet Rough-in Without an Existing Toilet

The toilet rough-in is very straightforward when the toilet isn’t there and the floor is bare. Here’s how to measure a toilet-rough in if you don’t already have a toilet installed:

  1. Identify the location of the drainpipe (toilet flange opening) on the floor. The drainpipe will look like a round hole cut out of the floor. The hole may have a white plastic lining; this is the toilet flange.
  2. Measure from the bare wall to the center of the toilet flange opening. If your wall has a baseboard, be sure to raise your measuring tape so it touches the bare wall above for a more accurate rough-in size.
  3. Check your work. If your measurement comes out as something other than the standard 12” or 10” rough-in sizes, it’s possible you measured incorrectly. Remember that the tape measure should extend to the center of the drainpipe (toilet flange) opening—no further and no less.

How to Measure a Standard Toilet Rough-In

toilet in a brown and white bathroom

However, you can also measure the rough in without having to remove your toilet to see the drainpipe below! You can measure this easily if there are visible base bolts and caps or if the toilet has a visible profile where the trapway path can be seen. Here’s how:

  1. Identify where the toilet is bolted to the floor. Look for small bolts or caps at the base of your toilet. These are usually located in the trapway on the back left and right sides of the fixture. If your toilet has a skirted design, look for any indication of where the toilet is bolted on either the side of the toilet or where the toilet meets the floor. Consider using painter’s tape to indicate where the bolts are located.
  2. Measure from the wall to the center of the toilet’s base bolts. Doing so will provide you the toilet’s rough-in distance.
  3. Avoid measuring from baseboards or other moldings. If your wall has a baseboard or other moldings, adjust your measuring tape so it starts from the bare wall just above the baseboard. If you have to, measure the width of the baseboard (the edge to the wall) and add that to the total measurement so it’s accurate.
  4. Check your work. If your measurement is something other than the standard 10”, 12”, or even 14”, double-check your work! You don’t want to make the expensive mistake of ordering the wrong rough-in toilet.

How to Measure a Corner Toilet Rough-in

Corner toilets can be a bit trickier than standard toilets when it comes to rough-in sizes, but have no fear! The follow how-to will provide you accurate results for a smooth installation:

  1. Identify where the toilet is bolted to the floor. Look for caps or bolts at the base of the toilet to find where the toilet connects to the floor below.
  2. Locate the toilet flange or drainpipe. Because the existing toilet is covering the toilet flange (drainpipe), you have to estimate its location based on the bolts you just identified. The toilet flange will be located at the centerpoint between the two bolts.
  3. Mark the toilet flange location on your toilet. For easy measuring, use tape or some other non-permanent tool to mark the centerpoint of the toilet flange. Your toilet flange is likely located between your toilet seat and tank.
  4. Measure from the center of the toilet flange to adjacent walls. Instead of measuring from the drainpipe location to the point (corner) where your walls meet, measure from the toilet flange outward at a perpendicular, 90-degree angle toward walls on the left and right of the toilet. You can use a measuring square or framing square to get the angle exact. Where both measurements intersect at the midpoint of the toilet flange indicates the rough-in size.

Rough-ins and Wall-mount or Rear-Outlet Toilets

wall mounted toilet in a white and blue bathroom

For wall-hung toilets, the flushed contents pass through the wall rather than the floor. You’ll need to measure vertically from the bare floor to the center of the waste drain to find the rough-in size of a wall-mount or rear-outlet toilet.

Other Important Toilet Dimensions

white toilet in a modern wood bathroom

Aside from the toilet rough-in dimension, another measurement worth noting when replacing your toilet is toilet height (or rim height) to ensure a proper fit in your bathroom and your comfort needs.

For toilet height, measure vertically from the floor to the rim of the toilet. The standard toilet height is 15”, though some toilets are as high as 18”-19” for comfort or accessibility. Toilet height does not include the lid and seat.

Bowl width and length might also be useful as well as they impact both space and comfort as well. Most toilet bowls come between 14 and 14.5 inches wide, though a rare few are made up to 16.5 inches.

Proper clearance surrounding your toilet is also necessary for comfortability and compliance with plumbing regulations. For example, the distance from other features should be measured from the center of the toilet flange (most likely the midpoint of the toilet, the same point from which you measure the rough-in to the wall) to the surrounding furnishings, like your vanity, cabinets, tub, or shower. The standard measurement for space around the toilet is about 15 inches, and 18 inches is spacious for added comfort.

The clearance from the front of the toilet will range depending on your local guidelines. Clearance of 21”—from the midpoint of the drainpipe forward—is required if the International Plumbing Code is the standard, whereas the Uniform Plumbing Code requires 24”. Check your local plumbing codes to ensure compliance.

For more useful information to assist in your hunt for a new toilet, check out our Ultimate Guide to Toilets or How to Choose a Bathroom Toilet to help you know the available options while shopping for a new toilet.

Just don’t forget to check your rough-in size first!