Creating a search utility that would allow someone to find the word count for any book has proved challenging. Both goodreads.com and amazon.com offer services that allow programmers to pull book data, such as Title, Author, Numbers of Pages, etc. But neither offers word count.
However, there are ways.
Option 1: Once upon a time Amazon offered "text stats" for a majority of their books. Included in these stats was word count. Amazon has appeared to have stopped this, which is unfortunate, since it's valuable for writers. Anyway, it is possible to obtain these text stats for most older books. Here's an example for Ender's Game http://www.amazon.com/Enders-Game-Orson-Scott-Card/dp/sitb-next/0765342294/ref=sbx_txt#textstats
That was nice, right? Now, it's hard to get to these stats, even for books that have them. But like I said, there are ways. Here's what you do. The number before the '/ref' is the key. Literally. So, find a book. Here's Into the Wild for example: http://www.amazon.com/Into-Wild-Jon-Krakauer/dp/0385486804/ref=sr_1_1?s=books&ie=UTF8&qid=1443569627&sr=1-1&keywords=into+the+wild (great book by the way). Grab the number before the "/ref" and insert that into the URL for Ender's game within the same location. Voila! Of course, if a book doesn't have text stats then it's not going to work; and most recent books don't.
Option 2: AR Book Finder. This site is a great resource for writers, despite the fact that we're not actually the target audience. If you've never visited the site, you'll be asked if you're a Student, Parent, Teacher or Librarian when first arriving. I consider myself a student of life, so I selected student and continued on. I suspect you're a student of life too, so perhaps you should choose the same. From this point, search for your book, click on the title within the list of results, and on the following page you'll find the book's word count. Yay! Unfortunately they don't have as extensive a book database as Amazon, but they do have most popular books.
Option 3: Buy the book and count each individual word. Come on, it would be fun!