It varies, based on my mental availability and the size of the book. For example, the longest book I read this year was "The Rest is Noise" by Alex Ross, about 800 pages, took me about one month, because I was reading other stuff at the same time, and because it's one of those books you need to slowly absorb. On the other hand, I can read a 200 page book in a day, although that's not what I usually do.