We are sprucing up a half bath. The toilet was squeezed in when we took it out... tank pressing against the wall. Now that we've added tile to the wall it will not fit.

The toilet rough-in measures 11" as it stands now. We feel that a 10" rough in toilet would solve the problem, but before we go out and buy a new toilet we want to be certain that the toilet we have isn't a 10". Since it was already a tight fit, we suspect it's a 12", but how can we tell for sure?