Here at BB we really discovered the awesome website How Long To Read which is helping bibliophiles everywhere figure out how many books they can read each month! The website is a sort of personalised calculator which can tell you how many hours it will take for you to read a particular book.
All you need to do is type the name of your proposed read/s into the website and search their catalogue. Once you've found the page for the book you'll see that it lists the average reading time for that particular title, but you can also get a better idea of how long it will take you to read by reading a sample paragraph whilst using their timer.
The sample text is usually the blurb for the book and as long as you read through it at your normal speed you should end up with, hopefully, a pretty accurate calculation of how long it will take you to read the whole novel!
Have you tried out How Long To Read yet?