My wife is having me redo our bathroom. We are replacing the flooring, vanity, toilet and a couple other things. I am trying to figure out which size toilet I should get. I have seen conflicting answers regarding how to measure my bathroom for a new toilet. It appears that the bolts on my current toilet installation are about 10.25 inches from the drywall and the tank sits right up against the drywall with almost no space. I have seen that most drywall is about .5 inches thick.

I would really like to get this toilet. I see that the rough-in for that toilet is 12 inches. Does this mean that the toilet would sit about 1.25 inches from the drywall and there would be a gap of 1.25 inches behind the tank of the toilet? Or does that mean that the drain size would be off and I would not be able to use this toilet even if I didn't mind the gap between the toilet and the wall.

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  • Your title (about rough-in) doesn't reflect your question (about toilet retrofitting) very well. I suggest revision so they match better.
    – isherwood
    Commented Dec 19, 2023 at 20:16
  • 1
    Is there a reason you can't simply get the 10" rough-in version of that toilet? totousa.com/… (I think this is it.)
    – Huesmann
    Commented Dec 20, 2023 at 13:43
  • I ended up getting the 10" toilet from toto after looking at these answers. Thank you all for the help! Commented Dec 20, 2023 at 18:25

2 Answers 2


You would need to relocate the drain pipe entry further from the wall (or the wall finished surface in the area of the toilet tank) to use a 12" rough-in toilet.

Assuming everything's honest (I've seen some variations in practice, but generally in the safe "does not touch wall" direction) a 12" rough-in needs (despite the "rough" term) bolts 12" from the finished wall surface.

It's not inconceivable for the variance on a particular sample of an 11" or 12" rough-in to end up 10.5" actual, (I have a 12" that my particular example of ends up quite a bit away from the wall) but you can't depend on that like you can depends on a 10" rough-in fitting.


A standard 12" toilet won't work. It would interfere with the wall.

You need a 10" toilet. They're fairly common as old-work scenarios are not unheard of and mistakes are made with new framing on occasion.


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