By genre, roughly

Thriller and commercial fiction favour short chapters — 1,200 to 2,500 words — which is why those books read fast. Forty to sixty chapters in a 90,000-word novel is normal.

Literary and epic fantasy carry longer chapters, 3,000 to 5,000 words, giving twenty to thirty in the same length.

Non-fiction chapters are longer still and fewer, usually eight to fifteen, because each one must carry a complete argument.

Why length matters more than number

A chapter break is permission to stop reading. Short chapters make stopping feel unnecessary; long ones make it feel earned. That is a pacing decision, not a formatting one.

Uneven chapters are only a problem when the unevenness is accidental. A three-page chapter after a thirty-page one is a hammer blow if you meant it.

What chaptering does to the audio and film editions

Chapters become the navigation of the audio book and the act structure of the film book. At the house rate of 155 words to a finished minute, a 3,000-word chapter runs a little over nineteen minutes — a long single sitting for a listener.

Retail storefronts expect one audio file per chapter. Very long chapters make files listeners cannot resume cleanly; very short ones make a file list nobody can navigate.

Asked and answered

How long should a chapter be?

1,500 to 4,000 words for fiction. Under 1,000 reads as an interlude; over 6,000 asks a great deal of a reader in one sitting.

Can chapters be different lengths?

Yes, and the best books use the difference deliberately as pacing.

Do chapters change what an audiobook costs?

No. Production here is priced on word count — 7.000000000000001% for audio, 12% for film — so chaptering changes the listening experience, not the price.