I basically just get started and either I finish the book or I don't. I try not to look at the page count (or with ebooks on my ereader I just know that the page count is entirely made up given it changes when I adjust the font size and so many of the ebooks these days have about 30-80 pages dedicated to extra fluff at the end after the actual book is finished)
I honestly don't know how long of books I normally read since I don't pay attention to that. I just grab what looks interesting and either I read and enjoy it or I don't