This is gonna be a long one, so hang in there:
As an author, you should not be concerned with how many pages you have, but how many words you require to tell your story. This is especially important when you start plotting out your book. Here’s why:
Each genre has its own particular “average” length. A great story can be written in 40,000 words, but it is probably going to leave the reader unsatisfied. They will notice that it is “short” even if it has been expanded to fit 400 pages. On the flip side, some stories may require 200,000 words, but most people won’t read them. It’s overwhelming to see a novel of epic proportions staring at you from your Kindle, Nook or bookshelf.
Genre lengths vary greatly depending on the source of the information. I am using the book “An Author’s Concise Guide to Genre Writing.” It was written in the 1990’s by two German authors and has not been translated into English at this time. I am using this because they did mind-boggling statistical analysis, surveying the word lengths of over 500,000 books in both English and German to come up with their averages. They also point out that they did not include the works of Stephen King, Tom Clancy and a handful of other authors when figuring their genre numbers because they were epic length novels and were the exceptions, not the rule.
Short Story: 17,500 words or less. With the flash fiction movement still rising, this number may seem very high to many short story authors, but flash fiction is a different beast than a short story. It requires less than 2,000 words.
Novella: 17,500 – 50,000 words. The length of the novella depends on the genre. Romance novellas tend to be closer to the 17,500 mark while Sci-Fi novellas tend to be closer to the 50,000.
Children’s Chapter Book (usually aimed at late elementary and middle school children): 25,000 – 35,000 words. Chapter books over 35,000 are usually reserved for late junior high students who are transitioning to Young Adult novels. They are just too long for the younger age groups. Harry Potter is the exception and not the rule.
Novel: 50,000 – 110,000 words. This varies by genre and will be broken down later in the post.
Epic Novels: Any novel over 110,000 words is considered Epic. This does mean that Stephen King, Dan Brown and Tom Clancy almost always write epic novels and they sell very well. Most of us are not these writers and so our epic novels will not sell nearly as well. If you find your novel in the area of 150,000 words or more, break it into multiple books and create a series.
Now, breaking down your novel length by genre…
Romance: Sorry, but these do tend to be the shortest. The average romance novel is 50,000-60,000 words. Although, I will add a note that there are hundreds of epic length romance novels that have done well in the past, but they tend to be historical fiction or science fiction based romance novels.
Mystery: 65,000-75,000 words. It is difficult to maintain the “who-done-it” aspect for more than 75,000 words. Most mystery novels that are longer have an extra 10,000-15,000 words that either introduce the characters in the beginning or have a long “wrap up and explanation” at the end.
Science Fiction: 80,000-90,000 words. Science fiction usually requires more explanation and universe building than other genres, so they tend to be longer novels. The setting and atmosphere must be created and in turn, this creates more words.
Fantasy/Urban Fantasy/Paranormal Fantasy: 75,000-85,000 words. Much like science fiction there is more universe building with these novels, therefore more words.
Action/Adventure: 60,000-70,000 words. Novels in this genre tend to be shorter because it is hard to run from action sequence to action sequence as well as the mini-climaxes and tension breaking areas. The highs must have lows and vice-versa. But when an action/adventure book gets too long, the building and releasing of tension becomes prosaic and people put the book down long before it gets finished.
Suspense/Thriller: 85,000-95,000 words. It takes a lot of effort to create suspense and much like science fiction and fantasy, a significant amount of atmosphere building is required. Hence the longer word lengths.
Chick Lit & Coming of Age: 65,000-70,000 words. This seems like a very narrow average, but since both are about the expansion of a main character as a person, I’m willing to go with the suggestion that the narrowness is because it is also about the same length as an autobiography (which are usually significantly shorter than biographies).
Historical Fiction: 90,000-120,000 words. This is the broadest average and leaks into the epic length novel category. Historical fiction has always represented a different type of story. The rewriting of history does require a significant amount of work, especially when the time period in question is well known to the general public.
Westerns: 100,000-110,000 words. Westerns are a specific piece of historical fiction; however, the popularity of “cowboy stories” has made them their own genre. Because it is historical fiction, you have the same relevant word counts. The writer must conform to the period of history and make everything authentic or they must rewrite the history of the time to conform to the story. As a result, westerns tend to be long.
Remember, these are only guidelines. Your story might be significantly longer or shorter than those listed above. Plus, there is a crossover factor. Very few novels fall into one genre. For example, most mysteries are actually mysteries, suspense novels and action/adventure novels, so they may require more words to build suspense or fewer words because you are running from action sequence to action sequence.
Also note that I did not include horror as a genre. The authors admitted when doing their word count averages that horror, true horror, was almost always either short stories (Lovecraft, Poe, Dickens) or epic novels (King, Barker, Shelley, Rice). They did offer that horror novels could be found, but they tended to be more about paranormal mystery or paranormal suspense or in the case of books like We, it is science fiction horror.