You would think this question would be one of those easy-to-answer-in-a-couple-hundred-words type questions. Unfortunately, it is not. In fact, there are so many considerations that I've decided to break up this answer into three posts in order to cover it all. :) The posts will include: 1) genre expectations for length; 2) story telling expectations that can override length; and 3) formatting decisions to give an appearance of shorter, longer, or just-right length.
First let me say that with e-books, length has no meaning. This is because e-book length changes from one device to another. It changes depending on how the reader configured the device for font and size. Even though you may have used Garamond 12 pt font when you compiled your EPUB or MOBI file does not mean that is what the reader sees. Some e-readers translate all fonts to Times Roman. Others provide a selection that the user may select. Then, of course, readers can enlarge the font or make it smaller. If there are images, tables, special headers, etc. that also changes from one device to another and form one user to another. Maybe one day the ubiquity of reading electronically will put the perception of length as it relates to value and price to bed. Personally, I would love it if we--the reading public--would stop tying value to length. I think it's moving in that direction but we are not there yet.
For the past four to five decades the use of mass market paperback (MMP) for most genre authors put forth a standard calculation of 250 words per page. In that case an 85,000 word book ended up around 340 pages. Up until about 10 years ago, a 340 page book was fairly average for most genre fiction in MMP. Today, 340 pages would be considered long by many genre publishers. All reader analysis in the past five years suggests most readers prefer shorter books now, around 250 pages or 55,000 to 75,000 words with many publishers looking for books in the 60,000-70,000 words range. In addition, MMP is used less and less by traditional publishers and is almost non-existent for self-publishers. Trade paperback (U.S. sizes are 5.5 x 8.5 inches or 6 x 9 inches) is the "norm" now which means the page count will be lower than it was in MMP.
When it comes to books, everyone has an opinion as to what is too long, too short, too hefty, not enough substance, and everything in between. For my own books I've had reviews that say the length was "just right" and "wished it were longer" and "wished it were shorter." All for the same book. Every reader brings expectations to the story, and a complaint about length is more often a complaint about not being fully satisfied with the story. However, there are some "average" expectations of length dependent on genre. But even then the range is wide.
Note: My follow-on posts on this topic will relate best to fiction. Though I also write non-fiction, questions of length and perception of value are very different from fiction and not as easily manipulated. A very slim non-fiction self-help book can command high prices if the readers believe it made a big difference in their life or they learned something the could not learn elsewhere.
Regarding Length Expectations, the statements below are not statistically sound. They are gathered from several blogs by agents, editors, and publishers. The numbers reflect a preponderance of agreement among them.
Note: An adult or YA "novel" is defined as 40K and up.
Picture Books - Picture books are generally less than 1000 words. About 500-700 words is he norm.
Middle Grade - Early middle grade (age 7-10) you’ll want to stay around the 20k-30k word count range. The average middle grade (age 9-12) is 30k-40k. Upper middle grade (age 10-13) can hit in the 50k word count range (possibly longer, if it's something really unique e.g., Harry Potter).
Young Adult - Young adult fiction allows for a lot of flexibility in word count. And as more than 50% of YA readers are actually adults, the expectation is often for higher word counts. Though it can be as short as 40K for the younger set (12-14), it tends to range from 55K to 90K with 65K-70K being the average.
- Mainstream YA - 45-75K
- Paranormal/Fantasy YA - 55-120K, but most often in the 75-80K range. If you are writing a popular series, the second or third book can go higher than the norm and readers will be okay.
- Mystery/Thriller - 75-90K
Adult Fiction - This one is the most difficult to get right because the pundits are all over the place. I suspect that is because of the huge variability among genres and types of offerings. In general, anything above 70k but less than 115k seems a safe range. The sweet spot for general adult fiction appears to be about 85- 90k. However, almost every genre has a "category" or subgenre of slimmer books. For example, cozy mysteries are significantly shorter than suspense mysteries, and procedurals are somewhere in between the two. In Romance, there is an entire sub-genre called "category" romance which run 55-60K and have few, if any, subplots outside of the primary relationship. And with reader trends tending to favor shorter books as a whole, it seems that the 55-75K range sells really well.
Below are some general word count guidelines:
- General Contemporary Romance - 65-100K, with 75-85K being the most desired
- Chick-Lit or Women's Fiction - 65-80K
- Paranormal/Fantasy Romance - 85-100k, again closer to 85K the most desired
- Category Romance - 55-75K with most often bought in the 55-60K range
- Historical Romance - 75-110K with most coming in at 85-90K
- General Crime Fiction - 90-100K
- Cozy Mysteries- = 65-90k, most in the 65-70K range
- Light Paranormal - 75-90K
- Historical - 80-100K
- Noir - 70-90K
SF/Fantasy/Horror - 75K-120K However, this is the hardest category to lock down and the subcategories often cross over, but below is a best guess.
- Hard SF - 85-110K
- Cyberpunk - 75-90K
- Space Opera - 75-120K, but tends to stay closer to 80-90K
- Epic Fantasy/High Fantasy - 85-120K
- Contemporary Fantasy - 75-100K, with most in the 85-90K range
- Urban Fantasy - 80-110K, with most close to 90K
- Slipstream - 75-90K
- Dark Fantasy/Horror - 65-10-0K, with most around the 80K mark
- New Wave - 70-90K
Being Indie means you get to determine what is the right length for your book, instead of pleasing an editor or agent that provides averages that meet their combination of cost and trends before understanding the needs of the story.
However, also keep in mind that readers have been trained to expect certain lengths over decades. Those expectations tend to shift with whatever are the bestsellers that year. Before Harry Potter, no publisher considered accepting a Middle Grade book that was so long. After Harry Potter every publisher was looking for longer fantasies.
Though reader trends do show that shorter books sell well, a good book will always outweigh length considerations. There are also other ways to offer a longer book, such as serializing it.