Well each page is 100mic roughly for 80gsm paper which is pretty standard. So if you did something like a 200 page book that is 20mm's which at 72 dpi roughly 54px's or roughly 27px's for a 100 page book.
That's excluding any cover page, which heavily depends on binding/hard cover/what ever else.
That's excluding any cover page, which heavily depends on binding/hard cover/what ever else.