Most adult novels fall somewhere around 70,000 to 100,000 words, but there is no universal correct novel length. Genre, audience and publishing format all matter. A useful rule is to write the length the story needs while staying reasonably close to what readers in that category expect.
Typical novel word counts
These are guidelines rather than laws:
Romance: roughly 60,000–90,000 words
Mystery and thriller: often 70,000–100,000
General contemporary fiction: commonly 70,000–100,000
Fantasy: frequently 80,000–120,000 or more
Science fiction: often 80,000–120,000
Historical fiction: commonly 80,000–120,000
Young adult: often 60,000–90,000
Middle grade: often 30,000–60,000
A 140,000-word epic fantasy will not surprise readers. A 140,000-word cozy romance probably will.
Does word count matter for self-publishing?
Yes, even when there is no traditional publisher imposing a limit. Word count affects reading time, editing workload, page count, spine width, printing cost, paperback price and reader expectations.
More words generally mean more pages. More pages increase print cost, which can reduce your royalty or force you to charge more for the paperback.
Words per printed page
There is no fixed conversion because page size, font, line spacing and chapter layout all affect the result. A book with the same 80,000 words can become noticeably longer or shorter depending on its typography and trim size.
That is why a real typeset page count is much more useful than a generic “words ÷ 250” estimate.
Don't pad the book to reach a number
Readers would rather finish a compelling 68,000-word novel than struggle through an 85,000-word novel containing 17,000 words of filler. Use genre ranges as a warning system, not a quota.
If your thriller is 38,000 words, investigate why. If it is 175,000 words, investigate why. But don't add or remove material solely because an online chart told you to.
Tracking book length in Author Magic
Author Magic lets you choose an intended book length when setting up a project and tracks the manuscript as it grows. Because the book is typeset during the writing process, you can also see a real page count instead of relying only on estimated words-per-page formulas.
That becomes useful later because page count affects things such as your paperback's spine, gutter and printing economics. When you're ready to publish, the same project can generate the properly sized interior and cover wrap around the final book rather than an early estimate.
KDP's rules change from time to time. Check KDP's own help pages for the current requirements before you publish.