This is the question I googled today: How long should a chapter be?
The concurring answer I received is, "The length of a string."
But is that really the answer? I don't think so. I visited many articles today and read about 40,000 word chapters and one sentence chapters. Writers can do what they want, but should they?
Below is a compilation of advice:
In adult fiction, the recommended chapter length is 5000 words or less. Why? Because adult readers average 20 minutes reading before bed. They like to end with a chapter break. The average adult reads 250 words per minute, therefor a chapter should not exceed 5000 words. (20 minutes x 250=5000).
A good time to insert a chapter break or a scene break is with a POV change, time change, or a scenery change. Help readers find a natural place to pause so they can eat, sleep, use the restroom!
Chapters are mini-stories and should feel complete with a beginning, middle, and end. Readers expect to be satisfied that the plot is progressing, but also left wanting more.
So after all this research, the answer is as simple as "the length of a string" or as complicated as a math equation. I prefer chapters under 3000 words, but I write for kids.
Overall, the key is to keep your reader in mind. Understand that your fans are human and need to stop reading at some point to take care of physical needs, or do homework, or chores, or turn off the light--so build in regular breaks, but keep the plot tension on high so they can't wait to come back to your story!