How To Rough In A Toilet

toilet rough in

A rough in is a term used to describe the measurements and plumbing required for a proper installation of a toilet. The basic rough in for a toilet will only cover the distance from the wall to drain flange. However, it is much more than that.

Depending on how much work is required (new install versus a repair, for example), you will need to rough in for the toilet, the water supply and possibly the drain, vent, and plumbing associated with the toilet.

This guide will cover all aspects of a toilet rough in so you are prepared for the project that lies ahead.

Before you Begin

There are two important factors that you must understand prior to starting this project.

First, most states require a permit for plumbing. You should seek professional assistance, or hire a plumber to do the rough in for you. If a permit is required and you do not wish to hire a professional, you must acquire the permits yourself.

measurement of a toilet bathroom

Second, this guide will cover the basic rough in dimensions for a standard toilet. It would be near impossible to cover every measurement for every toilet on the market. Because there are size restraints, handicap accessible stalls, and other factors that go into the final installation you will need to check with the manufacturer of your toilet to ensure you have the measurements required for proper installation.


This guide will, however, provide you with the rough in details that will cover the vast majority of toilets. A standardized guide, such as this, will not be able to determine your bathroom size, measurements, and accommodations. Some leniency on your part will be required.

professional plumber

Again, if you are ever in doubt, hire a professional to do the rough in for you. As this is just a guide, we will assume that the rough in will take place in an unfinished area. Safety must be adhered to, and this guide will not cover a new rough in for a finished area. (read: we don’t cover removal of tile, baseboards, etc.)

What Will You Need?

There are several things you will need, and this is just a brief overview. There are specialty tools you can use, or simply use basic hand tools. The choice is yours. However, you will need:

  • Drain materials using three inch PVC for downflow and 2 inch PVC for wet and dry vents.
  • Basic plumbing tools.
  • Carpenter tools including saws, hammers, and levels.
  • Generator (if using electrical tools and electric is not yet supplied to the area)
  • Markers, pencils and a tape measure.

You may find you need other tools, such as copper fittings for water lines. Ensure you have everything you need for your specific situation prior to starting the project.

Space Requirements

space requirements

The basic rule of thumb is 12 by 15 inches. All measurements are taken on a finished wall. The flange, for example, will mark the center of the toilet and will need to have clearance from both sides as well as front and back.

You need to maintain 12 inches from the back wall to the flange center and at least 15 inches on either side. The front spacing should be at least 21 inches, but in general, the front space won’t be an issue.

Before You Cut

flange for the toilet hole

You will need to make a hole for the flange in the subfloor. This is where the toilet will sit and be connected to the drain system. A toilet must have a three-inch drain without reductions. It should also be connected to a three-inch drain stack.

You also need to decide where the fixtures will be. You should maintain 15 inches of side clearance (unless unavoidable) from walls, cabinets, and fixtures. Knowing where the fixtures will be will assist you in the final measurements before you make a cut in the subfloor.

The Toilet Rough In

The first step of the toilet rough in will be measured at 12 inches from the finished wall. If the wall is not yet finished your measurement should be 12.5 inches. This will allow for the drywall to be installed without messing up the measurements.

Measure from the drywall and not the baseboards. All measurements are from the flat wall and not accents or wall ornamentation.

For Side Spacing

You will need to account for the finished wall. For example, if the finished wall will have tile over the drywall, you will need to account for this extra space.

The final measurement will be 15 inches plus finished wall to the center of the flange, from the sides, as well as 12 inches from the finished wall to the center of the flange from the back. Mark this area on the subfloor and double check the measurements.

Once the measurements have been verified use the toilet flange to center over the marking and trace the flange outline. Once you have the outline traced, this is where you make your flange cut.

Installing a Drain Underground

making a drain underground

From here you will either be installing a drain underground in which case you will need backfill or gravel to cover the pipe and provide a grade for the drain. If this is a second-floor install, you will need to cut into the existing drain stack and fit a T pipe to add the new drain.

Take note that cutting into an existing drain stack has dangers. Drains is connected to the sewer and collect and expel sewer gases. Since the rough in will need an inspection before the toilet installation, you should cover the drain access with a drain cover with rags.

Once the drain pipes and vent are in place and secure, you should have the end of the drain just below your subfloor where you cut the flange hole. You should ensure that all horizontal pipes support with hangers in four-foot increments.

Double Check

double check your work

You should also double check that all pipes have been glued and dried. If the pipes are only dry fitted, the drain isn’t complete. Capping it off with the flange will only cause the dry fit to separate, and the flange will need to be removed once again.

After verification of a glued and dried drain system, install the flange to the subfloor. Each flange will have toilet bolt mounting slots. These slots must be aligned with the sides of the toilet. Ensure that the slots are parallel to the side walls or fixtures and perpendicular to the back wall.

Secure the flange to the subfloor and the toilet rough in is complete. The inspector will need to inspect before finishing the flooring.

Rough In For the Water Supply Line

check the water supply

The final rough in is for the toilet called water supply line. The default spacing is measured outward from the flange and from the finished floor up to the wall.

The general guide is six inches from the center to the left (as you look at it facing the back wall). Mark this spot and use a ruler.

From this point, you will need to measure a minimum of six inches from the floor. However, depending on the type of molding or wall ornamentation is used to go as high as seven inches.

If the molding is the standard style, six inches will be sufficient. However, some bathroom molding can be as high as five and a quarter inches tall. Add half inch escutcheon, and you need to cut the frame to accommodate.

Using a seven-inch wall measurement will avoid unnecessary accommodations such as these.

In Conclusion

The measurements of a toilet rough in are the easy part. You have to do a lot of planning and thinking before making any cuts though. How the drain system will be incorporated, one of the major points that need to be addressed before the rough in.

You will also need to verify the finished space and where the walls and fixtures will be. These will ensure that you have proper clearance from the back wall to the toilet.

Once the rough in is complete, it will need an inspection. You should have acquired the necessary permits (if required in your area) and you have met all the requirements of the project.

Before you begin any work for yourself, you need to check with a professional to ensure that permits are required, and which ones should obtain. You will also need to find out if license requires the work.

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