How many book sales make a best-seller?

My wife and I recently attended an author talk and signing by the prolific and popular British author Julian Barnes. There was certainly no lack of interest in him and his books: the hall was packed and we were reduced to standing in the side-aisle, despite our having an official ticket. Barnes regularly appears in best-seller lists, and we got to wondering what actually constitutes a "best-seller" in this day and age. More specifically, we wondered how many books a week someone like Julian Barnes actually sold.
Best-seller lists, whether in newspapers or websites, never indicate just how many books were sold, and so, as usual, I resorted to Wikipedia, and their list of best-selling books. The page first describes the difficulty of obtaining accurate and realistic figures, particularly for older books. The Bible is estimated by Guinness World Records as having sold over 5 billion copies, and sales of the Qu'ran and Chairman Mao's Little Red Book probably also number in the billions. Old classics like Don Quixote, A Tale of Two Cities, The Three Musketeers, Les Misérables, Pride and Prejudice, The Adventures of Pinocchio, Alice's Adventures in Wonderland and The Odyssey almost certainly also belong on the list of best-selling books of all time, but concrete figure are impossible to find.
Among the stand-alone fiction best-sellers for which figures ARE available, top honours go to J.R.R. Tolkein's Lord of the Rings and The Hobbit, Antoine de Saint-Exupéry's Le Petit Prince, J.K. Rowling's Harry Potter and the Philosopher's Stone, Agatha Christie's And Then There Were None, Cao Xueqin's Dream of the Red Chamber, and Rider Haggard's She, each of which is estimated to have sold over 100 million copies. Following on are the ilk of C.S Lewis' The Lion, The Witch and the Wardrobe, Dan Brown's Da Vinci Code, all the other Harry Potter books, Paolo Coelho's The Alchemist, Gabriel Garcia Marquez' One Hundred Years of Solitude, Vladimir Nabokov's Lolita, Johanna Spyri's Heidi's Years of Learning and Travel, Lucy Maud Montgomery's  Anne of Green Gables, Anna Sewell's Black Beauty, Umberto Eco's The Name of the Rose, Jack Higgin's The Eagle Has Landed, Richard Adams' Watership Down, E.B. White's Charlotte's Web, J.P. Donleavy's The Ginger Man, Robert James Waller's The Bridges of Madison County, Lew Wallace's Ben Hur, and Johnston McCulley's The Mark of Zorro, all of which have registered sales of above 50 million copies each.
However, none of this gives me any idea of what a contemporary writer has to do get into the week's top 10 best-sellers lists. I have no idea whether, in Canada for example, a best-selling author sells 500 books? 1,000? 10,000? And it seems I am not the only person wondering. The Book Promotion Hub has done some homework on the subject, which reveals that each best-seller list has its own secret algorithm, and also that a first-week blitz is an important factor in the ratings. In general terms though, the article suggests that Amazon's Top 5 would typically sell over 7,000 copies a week, and that around 3,000 in a first week would get you onto The Wall Street Journal's best-seller list, and 9,000 onto the New York Times' list.
How this would translate to the Canadian market is unknown. I can only surmise that, with one-tenth of the population, dividing by ten is probably a reasonable guide, so maybe a paltry 500 - 1,000 copies would do it.
Another blog by a best-selling author suggests that 5,000 to 10,000 copies a week would probably get you onto the New York Times' Top 15 list. Bear in mind also that the time of year makes a big difference (for example, January is typically a low sales month, and September a high sales month, and the difference can be as much as a factor of two), and also that these figures refer to the relatively expensive hardback books that are typically released first, and the number of paperbacks sold are anybody's guess.
What I take away from all this is that "best-seller" is a notoriously slippery concept, which few people have a very good handle on. Add to this the notion that there are companies out there that specialize in getting your book onto the best-seller lists (for a price), that slipperiness becomes downright slimy and unpleasant.
It does at least give some idea, though, of just how few books sold constitutes a best-seller - in Canada, we are probably looking at less than 1,000 hardback copies sold, plus an unknown number of paperbacks. As for how many books Julian Barnes sold last week, I fear that we will never know.