MisterEight
I really wish there was a book sales equivalent to box office mojo. Would be super interesting to compare the numbers more in depth between super popular authors like yourself and less known/new authors.
Brandon Sanderson
There is, actually. It's called bookscan, and is generally only available to insiders. (But if you can find someone with access, you can track books back for two decades of sales info.)
Problem is, it doesn't track ebooks. (Because Amazon doesn't release them.) I wish this info were more public too, personally. But I can try to guess a kind of rough estimate, based on what I've seen. (This is for first year ebook/hardcover combined, and only applies to fiction books, and not those by a celebrity.)
On the chopping block: 5k (This is a book that did modestly well, but is probably overall losing money for the publisher. Some would keep publishing an author at this level, depending on expectations of growth, award recognition, or niche interest.)
Solid seller: 5k-10k (This is a book most publishers will always be pleased with, and will continue to pay a decent advance for. This author may not make a healthy living on their book unless they can do more than one a year, but will probably always have a writing career.)
High midlister: 10k-20k (This is an author who is well known in their genre, is a dependable seller, and has a dedicated--but small-fanbase. If you can find a writer with a number of books on the shelf, but they don't chart often on the NYT list with new books, they are probably in this category.)
Genre Bestseller: 20k-50k (This is a book that charts on the bestseller lists without hitting the #1 spot. Authors who hit this consistently set trends in the industry, are well known in their genres, and are pulling low six figure advances. Breaking out of this level and into the next takes serious luck, even in a field which already requires a lot of luck.)
Dominant Genre Bestseller: 50k-300k (These are the books that hit #1 on the bestseller list. Authors who do this consistently with each new book are generally at the top of their field, and are probably what you consider "super popular" in your post. But they--we, as this is where I am--are small potatoes compared to the next levels.)
Breakout Bestseller: 300k-1mil (These are books that "break out" of their genre, or are the top of larger genres, like thrillers. Teen books with a lot of momentum can hit here too. Books in this category sell in airports or walmarts to the general public for months, as opposed to those in the category below, which sell really, really well for one week--but only because fans buy their books week one, rather than waiting. I've outsold Dan Brown and John Grisham...for one week. The next week, they trounced me.)
Movie Books: 1-5mil (These are books from one of the other categories that have a film come out recently. Also, the tail end of the breakout bestsellers and the beginnings of phenomenon books. It gets really blurry in here as we're dealing with such large swaths of numbers. Game of Thrones books are in here, I believe. Note that they basically jumped over the category between, which often happens in sf/f when you get a film or tv show.)
Phenomenon books: 5-20+mil (These are books that somehow SUPER break the mold, for reasons nobody really understands. DaVinci Code. Harry Potter. Twilight.)