bookCALC is a very useful tool. It can be very helpful when you want to create a book using A4 pages split in 2 sheets.
You just type the number of your pages, click "calculate" and you'll get the result in 2 lines:
first line is the one side of your paper and seconds the other side. So you just copy and paste the results into page range of word and all the work is easy!

bookCALC is FREEWARE