The most important thing to recognize is the difference between your manuscript page size (which is most likely 8.5 x 11) and your published book trim size (which will most likely be smaller). When you discuss page count with your self-publisher, or per-page pricing, it is based upon the size of the published page, also referred to as trim size.
The most common published book trim sizes are 5.5 x 8.5 and 6 x 9, although on-demand publishing now offers most trim size choices available anywhere in the industry.
If your manuscript is 100 pages long at 8.5×11, you probably have closer to 200 pages of finished text when the book is published. Congratulations, your book just got twice as long.
That’s the good news. The bad news is, some authors are surprised when they see pricing based upon 200 pages instead of 100. Don’t be caught off-guard.
Keep in mind that your production price is directly related to your published page count. The more pages your book has, the more it will cost to print. Therefore, most authors keep their books between 100-300 published pages.
Yes, that probably means your book is already long enough to publish! But being long enough, and being finished are two different things, right?
Self Publishing Advisor 