It's The Question That Keeps Bookbinders Awake At Night...

... which seven-volume fantasy series which began with a fairly slim first volume got more and more lengthy as the end drew nigh: Jo Rowling's Harry Potter or Stephen King's Dark Tower?

Let's find out! Potter's in Blue, the Tower is Purple...

So - perhaps appropriately enough - the Tower has the highest numbers.

Here's a thought: how different would the current state of Bloomsbury publishers be if the Potter books had each been 324 pages long, and the series had run to ten books ?

I know that books, unlike many media, can be as long as they need to be to get the story told, but I'll wager that somewhere, a publishers' accountant has asked exactly the same question, though they probably followed it with a sigh, and then returned to crunching numbers.