If someone asks me what the number one mistake people make when they buy a new toilet, I usually tell them it’s the wrong rough-in dimensions.
It’s essentially impossible to install a new rough-in which doesn’t fit your current bathroom set-up.
In other words, unless you’re planning a new bathroom renovation with a new plumbing system, then you’re going to want to get this step absolutely right – because you can’t exactly return a toilet to the store!
So, to avoid paying for things you do not need to, I’m going to help you out.
If you’re stuck working out how to do the toilet rough-in, then read my guide below to find out everything you need to know for the perfect job!
What Is A Toilet Rough-In?
Okay, so I should probably first start with the basics before I dive right into the guide.
If you’re not familiar with the term, a rough-in of a toilet refers to the distance between the wall and the middle of the toilet drainpipe (the toilet flange).
By accurately measuring the rough-in, you ensure that there is adequate space between the drainpipe and the wall for the back of your toilet and the toilet tank.
This is to make sure that everything will fit perfectly when it is installed.
A toilet rough-in needs to be your priority when you buy a brand new toilet, so this is why I’m so keen on ensuring that you know what to look out for!
The Four Main Things To Remember
Before you start on your roughing-in, you’ll need to bear four main points in mind:
- The distance to set the toilet flange to the back wall
- The right clearance left to right
- The space you need to leave in front of the bowl
- The location of your cold water supply line
As I’ve said, getting these measurements exactly right is critical – if you put the toilet too close to the wall, you could find yourself paying out for a whole new toilet – not to mention maybe fixing some breakages and needing to dispose of the first toilet!
The Four Dimensions
I’m going to show you the four dimensions and how you get the measurements just right for your rough-in. I’ll break it down as simply as I can.
 The Distance To Set The Toilet Flange From The Back Wall
It’s first important for me to tell you that you need to take your measurements from the finished wall and not from the base molding. The center of the toilet flange needs to be twelve inches from the back wall.
There are a few precedents though. If you’re measuring from stud walls, you need to account for the thickness of the wall.
Drywall is normally half an inch – so if this is the case for you, the measurement must be 12 ½ inch measured from the stud wall.
This is going by the assumption that we’re measuring with a standard toilet, which has a 12 inch rough-in measurement.
The reason I say this is because there are some toilets which can have a ten inch or even a fourteen inch rough-in.
It’s worth knowing this because if you are replacing your toilet and the center of the toilet flange is ten inches from the wall, you do not need to move the flange at all, you can just get a toilet with a ten inch rough-in. Problem solved!
 The Clearance From The Toilet’s Center To The Sidewall
The critical thing to know here is that the minimum measurement is fifteen inches. You must have at least this amount of space from the toilet’s center to any wall – or any adjacent fixture if that is the case.
I’ll give you an example. If you have a bath vanity by your toilet, you’re going to need to keep fifteen inches of space. The same applies if your bathtub or a wall is next to your toilet – you will still need to keep fifteen inches of space.
Of course, you will always need to bear in mind the thickness of a stud wall if this is applicable. If you need to do this, you will also need to add it all up and then add it to the fifteen inches minimum.
 The Measurement Between The Front Of The Toilet To Obstructions
This step is a little tricky because it will depend on which plumbing code you’re in.
The International Plumbing Code says you need about 21 inches of clearance, whereas the Uniform Plumbing Code says 24 inches of clearance.
You measure this from the front edge of the toilet to any sort of obstruction, like a door for instance. This measurement is not to include an open door, but just so that someone can use the toilet facility whilst the door is closed.
Albeit if you wish to leave more space, then this is up to you, but many bathrooms cannot allow for huge amounts of clearance.
 Locate The Cold Water Supply Line
You measure this from the center of the toilet flange. Go six inches to the left and then up seven inches above the floor – which usually clears most of the base molding.
If the water line comes in too low, it looks awful – so it needs to be just right to avoid any unnecessary trimming.
The Bottom Line
And that’s everything you need to know about the toilet rough-in. Personally, I would recommend hiring a professional to perform this job so that you do not risk any further and unneeded spending.
However, if you can get this right, you can find yourself saving quite a bit of money and you will know how to do it next time!