I've taken some common books sizes and found their average weights. I did 2 common sizes for Hardcover books and since paperbacks are a little more varied I did 5 sample sizes. I've listed their averages by Dimensions/Pages/Weights.
LxWxH in inches/Avg # of Pages/ Size and Average number of pages in a Hardcover/Softcover book.
8x6x2/ 735pgs- 1lb 15oz avg
8.5x5.5x1.5/460pgs- 1lb 2oz avg
9.5x6x1--/370pgs- 15oz avg
8x5x1.5/760pgs- 1lb 3oz avg
7x4.25x2/1360pgs-1lb 5oz avg
7x4.25x1/590pgs- 9oz avg
6.5x9.5x.05/160pgs- 15oz avg
I'll try to post some average weights of school textbooks, next!