When you’re starting out writing, or indeed a way into your writing life, it’s always good to know what word counts you need to aim for so that you write a book that can meet readers expectations. However, always keep in mind that these are guidelines and come from the traditional publishing world. For me, a story should be as long as it needs to be for it to be told well.
Fantasy books tend to be longer than your standard book, this is because a lot of world building needs to take place for the reader to fully indulge in the work and believe the world and story. Therefore, word counts will likely run to the 110-120,000 wordmark. But, if you look at authors such as J.K. Rowling and George R. R. Martin, their books far exceed this but they’re normally the exception rather than the rule.
Sci-fi again tends to be on the longer side, running up to 100,000 words, however, in the indie market this can differ. My first sci-fi book came in at 76,000 words as the first book in a series, while shorter than average it was the length the book needed to be, which is also important to remember.
Romance seems to be anywhere from 40,000 to 70,000 words in length, mainstream novels tend to run from 70-100,000 words
Crime/Thriller has a guideline of 90,000 words, however, well-known indie writer J.F. Penn, writes up to 70,000 words and still has success, as do many other indies who write shorter pieces
Young Adult books again can vary depending on traditional or indie and by author, however, a general rule of thumb is 65-70,000 seems to be okay for YA books, although a lot of YA readers do also read longer books if the story is good enough.
Middle Grade is aimed at a younger audience so your book is going to be shorter, 25,000 – 40,000 is a good range to write in.
Flash Fiction, normally published by journals or websites, runs up to the 250-word mark or lower.
Short Stories depends on what you’re writing and if it’s for a magazine or a competition. Usually, you’re given guidelines by the organisation but typically, short stories will run anywhere up to 5,000 – 7,000 words and will be a complete scene. To have an idea of how short stories are written, why not read a couple of anthologies such as the Great American short story collection.
Novellas are the next step up from short stories and tend to run to the 17,000 word to 40,000 words and are a viable option if you’re self-publishing. Authors such as James Patterson are even getting on the bandwagon with novellas and they’re a great way to add extra titles to your series or author name.
Above is a guideline only, my general thoughts is that a book should be as long as it needs to be to tell the story. The word-counts should provide an indication of what to aim for rather than be a finite total. When I’m first drafting I aim for 60,000 words but always intend to write over (as my genre is sci-fi), but it will also depend on whether you’re going to be publishing traditionally or independently. If you’re going indie, then you have more control over your word count, but if you’re after the traditional deal, then definitely aim for the guidelines.
A good site to check out is Perma Bound, a site that has word count information for a lot of published books, so if you’ve got a book that you like the length of and want to know exactly how long it is, this site could help.