A toilets rough in is the distance from the finished wall behind the tank to the flange. There are a few measurements you need to consider. These include:
Grab a tape measure. You're going to be measuring the distance from the wall located behind where the tank will be to the center of the waste outlet. DO NOT measure from a baseboard or any type of skirting. You should only be noting the distance from a finished wall. If you already have or planning to put some kind of framing or a stud wall in, you need to take into account how thick that wall is and apply it to the final figure.
Many of you reading this will discover yours is 12 inches. This is seen as the standard and most common option, and there are many toilets built for this size on the market.
However, some bathrooms will require either 10 inch or 14 inch. While less common, there are also some great options available. See below for more information.
The great thing about this, is that you don't have to move your flange if it doesn't quite fit the standard size.
You don't want anything sitting too close to the edges of the bowl. Not only will it make the bathroom space feel more enclosed, it will also will make it hard to move around in your bathroom. And lets face it, this can be a hazard.
In simple terms, you want 15 inches minimum clearance around the bowl. This means if you've got a wall to the left, your outlet needs to be 15 inches away. The same applies to any vanities, sinks, and shower bases.
When it comes to bowl depth, and how much clearance is required in front of the bowl, this varies. It completely depends where your located and your plumbing code. The International Plumbing Code says you need 21 inches. The Uniform Plumbing Code is even more at 24 inches. Instead of measuring from the flange, this is taken from the part of the bowl that extrudes the furthest from the wall.