Here's a handy cheat sheet of common fiction categories (word count information comes mostly from this helpful Literary Rambles blog post):
Note: In the publishing world, length is determined by word count rather than pages, since the page count will change depending on how your manuscript is formatted.
- Board Books: Books with thick cardboard pages, intended for babies and young toddlers. Generally under 100 words.
- Picture Books: Books written for children from ages 3-8. Illustrations are very important to the story (and are often on every page). Generally 400-900 words in length.
- Early Readers: Books designed for children who are beginning to read on their own, or from about ages 6-8. There are only a few sentences on each page, and they usually feature color illustrations. Generally 200 to 3,500 words in length.
- Chapter Books: Books for independent readers who are a little older, about 7-10. Sentences are a little more complex in these books, and they may have no illustrations at all. Generally 4,000-10,000 words in length.
- Middle Grade: Books for readers from ages 8-12. The word count starts to vary a little more widely here. Generally 25,000-45,000 words in length, but sci-fi or fantasy books that might require more world building might go up to 70,000 words or even higher.
- Young Adult: Books written to appeal to readers over age 12. (Notice there's no upper age given for YA--that's because this genre appeals to a lot of adults, too!) The word count for YA books is generally in the 45,000-70,000 word range, but speculative fiction books may go as high as 100,000 words.
- Adult: Books written for the adult market can be all over the map. This Writer's Digest blog post suggests that 80,000-90,000 words is a safe range, but also mentions that books as low as 70,000 or as high as 110,000 will probably be all right. As with Middle Grade and Young Adult books, sci-fi and fantasy novels tend to run a little longer, so acceptable word count for these genres is probably more in the 90,000-125,000 range.
Check out the linked blog posts above for more information!