Understanding Toilet Rough-In Measurements: A Detailed Guide

Understanding Toilet rough in measurements can be very confusing. In fact, many online guides get it wrong. This is partly because there are two parts to choosing the right toilet rough in.

  1. You need to measure the rough in measurement of your bathroom
  2. You then need to find the right toilet to fit in that rough in space.

Many people confuse these two steps and this is where most of us go wrong.

We can all agree that your toilet rough in measurement starts from the wall to the center of the drain hole but what confuses people is the rough in size of the toilet that should fit into that space.

This guide will help you understand what a toilet rough in is, how to measure it, and which toilet size will fit into your rough in measurement.

What is A toilet rough in?

A toilet rough in is the distance from the finished wall behind the toilet to the center of the drain hole on the floor. However, it can also refer to the rough in of the toilet itself which indicates the type of rough in space that the particular toilet will fit into.

Most modern bathrooms will fall within the 12-13″ range to accommodate a standard 12″ rough in toilet.

The rough in measurement for the toilet itself will be 10″, 12″, or 14″. With the 12″ models being vastly more popular than the other two. However these numbers designate the space the toilet will fit into, not necessarily the measurement to the center of the drain to the back of the toilet.

How to measure your toilet rough in

There are two ways to to get the correct rough in measurements for your toilet.

1. Measuring the rough-in for the floor when the toilet is installed:

To measure the rough-in for the floor, start by placing a measuring tape against the wall behind the toilet. Measure from the wall to the center of the drain hole on the floor. This measurement will give you the rough-in opening for you toilet to fit into.

2. Measuring the rough-in of your existing toilet while it’s installed:

To measure the rough-in of your existing toilet, start by measuring from the wall behind the toilet to the center of the floor bolt that secures the toilet to the floor. This measurement should be accurate as toilet manufacturers strategically place the bolt cap parallel to the center of the drain hole to indicate where it’s located when the toilet is installed.

How to know which toilet size will fit in your rough in measurement

As we mentioned earlier, the toilet rough in measurement can be anywhere from 10″ to 16″. However, when shopping for a toilet, you will soon realize that they only come in three varieties

  • 10″ Rough- in Toilets
  • 12″ rough in toilets
  • 14″ Rough in toilets

This is because it’s always assumed that there will be a gap between the finished wall and the back of the toilet. While this gap may vary from case to case, it’s best to keep it around 3/4-1″. It should definitely not be any more than 2″.

It’s important to note that the gap is usually assumed in the manufacturer spec sheet and you should refer to that sheet to see their assumed measurements

For example the two diagrams above assume two different measurements for the gaps behind the tank: 3/4″ for the Kohler toilet and 1″ for the American Standard.

When installed, the Kohler toilet will have less of a gap compared to the American Standard toilet, while the latter will be more forgiving should your floor rough in be less than the assumed 12″.

12″ Rough Toilets are the Standard and the most popular

While you can find plenty of bathrooms set up for a 10″ rough in older homes in the Northeast of the US, 12″ rough in are by far the now the standard. Plumbers are encouraged to rough the newer and remodeled bathrooms for 12″.

Therefore, when shopping for a new toilet, it’s always assumed that you’re looking for a 12″ unless otherwise specified. This is clearly shown by the total number of toilets available in 12″ compared to the alternatives.

Every single collection of the top manufacturers is available in 12″ while top brands only leave a few models available in 10″ or 14″.

Shopping for 10″ & 14″ Rough in Toilets

Shopping for a 10″ and 14″ rough in toilet can be quite frustrating as manufacturers see those measurements as an afterthought. They are in fact a derivative of an existing 12″ toilet. Unfortunately, for most manufacturers, it’s typically the most basic of their toilet collections, although this is starting to change.

# of Collections for each Brand 10″ Rough in Toilets12″ Rough in toilets14″ Rough in Toilets
American Standard4231

*For Toto Toilets, we only picked the toilets with the exposed trapways, as Toto uses a rough in kit for their skirted toilets.

It’s important to note that the basic collection for all toilet manufacturers is typically a generic looking 2 piece toilet. Two piece toilets are sold by the components: Tank & bowl , & toilet seat are sold separately.

Here are the actual collections used for each of the top 3 brands for 10″ and 14″ toilets

  • Kohler 10″ rough toilets: Highline, Highline Classic
  • Kohler 14″ rough toilets: Highline & Wellworth
  • Toto 10″ rough toilets: The Drake Collection including Eco Drank & Drake Transitional
  • Toto 14″ Rough toilets: There are no 14″ collections available for Toto unless you count the skirted toilets with the rough in kits (more on that later).
  • American Standard 10″ rough in toilets: Cadet, Reliant, Edgemere, Colony.

All these toilets are best sellers in 12″ rough versions. So the toilet companies focus on those to convert into a 10 or a 14″ rough. There are two ways for manufacturers turn their existing 12″ toilets into a 10″ or 14″ toilet

  1. By Changing the size of the bowl
  2. By Changing the size of the tank

Changing the size of the bowl

With this method, the tank of the two piece toilet stays the same while the bowl is interchanged from a 12″ bowl to a 10″ rough in. With these types of toilets, the tank typically sits flush with the bowl., as seen in the Kohler Highline below.

Converting 12" rough toilet into 10" and 14" by switching the bowl

It’s important to note that, in this case, switching to a 10″ rough toilet, doesn’t change the over front to back dimensions of the toilet. Instead, the company simply manufactures a different bowl and relocate the drain hole underneath. This is why, the tank stays identical to the 12″ toilet, while the bowl needs to be a different SKU.

Changing the size of the tank

With this method, the toilet manufacturer sells one SKU of the toilet bowl, and instead has three different skus for the toilet tanks. WIth these toilets, the tank typically hangs behind the toilet bowl. See the diagram below.

Changing the tank to convert 12" toilet into 10" or 14" toilets

The toilet bowl needs to be positioned further back for 10″ rough toilet, as its tank is much slimmer than the 12″ tank. For the 14″ tank, the bowl needs to be positioned 2″ further forward compared to the 12″ to accommodate its much thicker frame.

How Toilet Manufacturers are Producing more 10″ and 14″ toilets with the Toilet Rough in Kit

As we mentioned before, 10″ and 14″ rough in toilets are an afterthought for most toilet manufacturers. They are reserved for their entry level toilet that are often a 2 piece toilet and fairly generic looking. However, this has been changing in recent years due to the use of the toilet rough in kit.

The toilet rough in kit is a piece of plastic that has offset openings; one end connects to the existing drain hole on the floor while the end that is positioned slightly forward (14″ rough in kit) or backwards (10″ rough in kit) connects to the toilet opening. See diagram below

With this kit, manufacturers can focus on producing strictly 12″ toilets and add this as add-on for homeowners who need them for their niche use cases.

However, it’s important to note that this kit only applies to newly manufactured toilet specifically made to work this kit and are not compatible with existing toilets.

These kits have allowed popular brands like TOTO and Kohler to offer more one piece toilets in 10″ and 14″ options.

Other rough in dimensions for Floor Mounted toilets

Other than the typical toilet rough in from the wall to the center of the drain, there are other important measurements for the installer to consider when roughing in a toilet. Specifically, there are two measurements the Uniform Plumbing Code (section 402.5) that they have to follow in order to meet code.

  1. The side to side clearance from the toilet to the nearest wall, or any other obstruction (i.e vanity or another plumbing fixture.
  2. The Clearance Space from the toilet to any obstruction in front of it.

Side Clearance Space for a Toilet

When installing a toilet, the installer needs to make sure that there is enough space around it to allow for comfortable use and maintenance. The Uniform Plumbing Code requires a minimum of 15″ of side clearance space from the center of the toilet to any adjacent obstruction on either side. This clearance ensures that the user of the toilet got enough space to sit and use the toilet comfortably. After all, most people’s take up way more space than the width of the toilet tank.

Front Clearance Space for a Toilet

The front clearance space is the distance between the front of the toilet bowl to the nearest obstruction, this can be a wall, or a vanity/sink fixture. This space is to be no less than 24 inches according to the Uniform Plumbing Code. This distance can vary with different international codes but UPC is what is used in the USA.

Rough in Dimensions for Non Floor Mounted Toilets

So far, we’ve been solely focused on rough in measurements for floor mounted toilets. However, there are also rough in measurements to consider for non-floor mounted toilets, wall hung toilets and Rear Outlet toilets.

Rough in Measurement for Wall Hung Toilets

The Rough in measurement for wall hung toilets is measured from the floor to the center of the drain hole. However there is not a set standard, as the installers are mainly concerned about achieving the right height desired for the bowl: Either Standard Height or ADA Height.

With that said, it’s still important for the installer to look up the measurements of the manufacturer to know exactly where the drain hole is located in relation to the rim of the bowl. As this is where the inlet for the carrier will need to be installed in order to connect to the wall hung toilet.

Rough in Measurement for Rear Outlet toilets

Rear Outlet also known as Back Outlet toilets have a standard rough in measurement of 4″. All manufacturers that we have come across adhere to that standard and so far we have yet to witness any outliers.

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