Those who are new to Christianity might sometimes ask the question. There is no need to be surprised about that. We are not born in the world where Christian message would be all around us. Some of us have not heard a single message from the Gospel and have no idea what Jesus did for us before we really got converted. So, how do we know what books are in the Bible, what Old and New Testaments are, to say nothing of the number of pages the Bible has!
Well, to tell the truth we cannot exactly answer the question. The most correct answer would be: a lot of. The fact is that there is a multitude of Bible versions and those versions have different number of pages. It does not mean those Bibles are different in terms of the number of Biblical books they contain or the Canonical content that they have. No! But some might have a lot of commentaries, others might not. Some might have study guides and parallel verses and etc.
Most Bibles have over one thousand pages though. Hope the answer satisfied your curiosity. Sorry for not being more exact, but it is not easy to do that.