Each book has a different size, depending on the Facebook user. The best way to know how many pages you will have is to try it out (It's free to create it). You can increase or decrease the number of pages by lengthening or shortening the timerange.

We advise you to start with a small timerange and increase it progressively.

The dimension of the book is 8x10" (20x25cm)
For quality reason the limit is 500 pages per book (it makes a book about 4.4 pounds (2 kilograms), and 2.8 inches (5 centimeters thick).
Except for the Luxury book who is limited to 250 pages also for quality reason.