The terms "auditorium" or "grand auditorium", as well as "concert", "grand concert" etc. are generally referring to the size of guitars, rather than their shapes. I think the misunderstanding begins from Taylor started using these terms to describe their guitar shapes; but size-wise, Taylor's understanding is a bit different than other brands (i.e. Martin and its derivatives). For example, Martin considers its Size 0000, or "M" series guitar as grand auditorium size, but Taylor's Grand Auditorium designs (*14) are a bit bigger than that.
Since Taylor's naming convention is also becoming a standard nowadays, it's actually a shoe-size problem. So the question here is, which standard will you adopt? Then you can measure the guitar yourself and look up Martin's Size Chart or Taylor's to answer your question.