A question that writers get asked a lot is “How long should I make my chapters?” Usually, the response is “as long as it needs.” Not exactly a lot of help.
Personally, I find that about 2,000 words is the right amount. A page (for a 4″ X 6″ book) is about 150. So, a two thousand word chapter is about 13 pages long. Most people can focus on a single task for about 50-60 minutes, which is why meetings or classes are usually an hour long. Any longer and people need a break. For me, I can read about a page a minute. This means I can read about 60 pages before needing a break (this can change depending on how interesting the story is).
You want to take into account page numbers. If the reader sees that every chapter is 30 pages long, they might put the book back on the shelf. But, the same can be said for too short of chapters.
Next, you want to think of a chapter as a mini-book, or a longer paragraph. You want to contain an idea or scene into one chapter. That doesn’t mean the characters can’t change locations or times, but the action should connect. For instance, the adventure character can say, “We need to reach the jungle outpost before continuing,” and then have a time skip to them at the outpost. The events should all connect to same “scene” (i.e. them getting ready for the journey). Each chapter should have a “beginning,” “middle,” and “end.”
Usually you want a chapter to end on a mini-cliffhanger. For instance, the spy hero uncovers the plans for the doomsday device but gets bonked on the head.
Another time you might want to end a chapter is when the point of view changes for a long period of time. If the change is like a paragraph or page long, you don’t need a new paragraph. If the POV changes for multiple pages or chapters, it’d be a good idea to start a new chapter.
If you are going to have long chapters, you should consider adding breaking/resting points. A lot of readers like to read to the end of a chapter before stopping (because it makes it feel like you completed something–also you can usually remember where you left off); but if the chapter is going to take a long time to finish, they’ll get frustrated. If you add breaks, such as time shifts, it’ll give the reader a chance to stop and process. If you do a break, it should be visual so that the reader can say, “Oh, I stopped at the little flag [or asterisks or whatever].”
So, the answer to “how long should my chapters be” is still vague. There is no set number–it does depend a lot on the writer’s style and message–but you also need to think of the reader. How much are they going to put up with? You need to make it as easy and enjoyable for them as possible. You aren’t going to please everyone–some people like really long chapters while others want very short chapters–but hopefully you’ll find the right readers for your story.
Writing is as much a science as it is an artform. It takes years of practice and study to master…and even then you get it wrong.