How to Measure a Toilet Rough-In

toilet that was roughed in
Installing a new toilet or replacing your old one can be a daunting project. With so many styles, types, and sizes of toilets, picking the right one for your bathroom is not easy.
Luckily, with a few measurements, you can find a toilet that is a perfect fit, whether for your main bathroom, guest toilet, or office lavatory. However, picking out a toilet style is the first step. Making sure it’s the right model and positioning it correctly in your bathroom takes different skills altogether!
You will need what builders call the toilet rough-in measurements, which include the toilet flange’s distance from the wall. Read on for specific instructions on how to measure the toilet rough-in so you will be sure to get the right size.
While this can be a DIY job, it is also somewhat complicated, so if you find you need help, don’t hesitate to call us at MT Drains and Plumbing for professional advice or help if you live in Vaughan, Ontario, or the Greater Toronto Area. Contact us at 905-761-5551.

Table of Contents

Three Basic Toilet Rough-In Dimensions

A toilet rough-in positions the toilet over the water outlet beneath the toilet. The rough-in measurement is the distance from the wall (behind the toilet) to the center of the water pipe. Rough-ins usually come in three standard dimensions–10”, 12”, and 14,” with 12 inches as the most common length.

10-Inch Rough-In Toilet

If your space is limited because you live in a smaller apartment or older home, chances are that your toilet rough-in is 10 inches.

12-Inch Rough-In Toilet

A 12-inch rough-in toilet is the standard size on the market and probably the most common one you’ll find when buying a new toilet, since many buildings and houses are set up that way.

14-Inch Rough-In Toilet

While the common 12-inch rough-in toilets set the standard in this industry, sometimes they won’t fit your home, leaving a large gap between the tank and the wall. If you want to reduce that gap behind the toilet tank, consider getting a 14-inch rough-in toilet.

Toilet Rough-In Measurements You Need to Know

Organizing well goes a long way towards picking the perfect toilet. Before roughing-in a new toilet, you need to know a few measurements:
  • the distance from the back wall to the toilet flange
  • the clearance from left to right
  • how much space you have in front of the bowl
  • where to position the cold water supply line

Determine the Toilet Flange’s Distance From the Wall

Taking the right measurements before toilet installation will save you a lot of time and trouble. Ideally, you’ll want to set the center of the toilet flange 12 inches from the back wall—be sure to never measure from the base moulding. If you measure from stud walls, don’t forget to calculate-in the wall’s thickness. In most houses and buildings, drywall adds a half-inch, so the measurement for toilet rough-in from a stud wall will likely be 12 ½  inches. Remember that toilets may also come in 10-inch and 14-inch rough-ins, so calculate carefully to make sure you have the correct toilet.

The Clearance From Left to Right

When taking the toilet rough-in dimensions, don’t forget to calculate the clearance from the sidewall (or added fixture) to the center of the toilet. Usually, the measurement is 15 inches, but some toilets are larger. When measuring, make sure to leave a minimum of 15 inches of clearance from the sidewall to the center of the toilet both on the left and the right (15 inches to the left + 15 inches to the right).
To clarify:  if a wall, tub, or bath vanity is near your toilet, you will need at least 15 inches of clearance from the center of the toilet.

The Space in Front of the Bowl

Another measurement you need to consider is the distance from the front of your toilet to any object or barrier it faces. The space in front of the bowl also depends on the plumbing code. If your local jurisdiction is under the International Plumbing Code, you will need a minimum of 21 inches of a gap. If the jurisdiction is under the Uniform Plumbing Code, you will need 24 inches.
The clearance in front of the bowl is measured from the frontal toilet edge(not the center, as the earlier measurements) to the cabinet, plumbing fixture, walls, or a door.

The Location of the Cold Water Supply Line

Whether you are replacing or installing a new toilet, the position of your cold water supply line is vital. Water supply lines vary in size and length, so it is better to know how to measure toilet rough-in correctly so you will purchase the perfect toilet for your bathroom.
So, where to position the water supply line? Is there a formula that can help you determine the perfect location?
Measure six inches from the center of the toilet flange to the left and seven inches above the floor. According to professional plumbers, this is a common height because it suits most toilet sizes and clears most toilets of base molding (a big problem among homeowners).

How to Measure the Toilet Rough-In

With an Existing Toilet

Most people will want to measure the toilet rough-in while they still have the old one attached to the ground. The good news is that toilet manufacturers have made it super-easy for us to take toilet rough-in measurements, because the bolts that hook up the toilet to the floor are positioned directly in the center of the plumbing.
You will see two bolts (most of them have caps). Measure the toilet distance from the wall to the center of the bolts. That measurement is your toilet rough-in.

For a Renovated Bathroom

If you are redecorating your home, you might have removed the old toilet. Don’t worry—you can still take the toilet rough-in dimensions and purchase the right toilet for your bathroom.
First, locate the circular pipe opening (located under your house) and measure from the center of the pipe to the wall. Don’t measure from the back or front of the pipe, but from the middle.

On a New Foundation

If your house is still in the building process but you want to get a head start on your plumbing and furnishings, it is possible to measure the rough-in. You need to measure from the middle of your plumbing to where your wall will be (it’s easier if you draw a line).

Call Us for Help

Prepping your bathroom for a new toilet shouldn’t be stressful. If you find measuring a toilet rough-in difficult, contact MT Drains & Plumbing at 905-761-5551. Our professional plumbers have been offering plumbing services since 1991.
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Paul S

Paul has more then 20 years in basement waterproofing and plumbing projects experience. Looking for an advice from an expert plumber? Make sure to read Paul's articles about residential waterproofing and plumbing projects in Toronto.

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