Writers often ask that question. I asked that question when I first began writing Bryony. Online searches (at least in 2008) weren't very helpful. "As long as it needs to be," was the most common response.
So I set a guideline for myself: 3000 words. If a chapter was significantly less than 3000 words, I re-examined it. Now I am not saying all chapters need to be 3000 words; that was just MY guideline (and for the novels in the BryonySeries, it still is).
Here are the questions I would ask myself if the chapter ended up with less (or even significantly more, which none of those early chapters did) in that first novel:
* Is it sufficiently developed? Are the points I wanted to make, well-made, of did they require fleshing out?
* Does it contain enough information to stand on its own as a chapter? Would it be better served as part of the preceding or subsequent chapter?
* In the case of long chapters: Does it need to be broken up?
If a short or long chapter passed this test, it stayed. Otherwise, I started cutting into the prose.
Ultimately, it's not the length of a chapter that makes or breaks it, but the purpose for the chapter. In Before the Blood, I have some chapters that don't reach 2000 words. The largest just top the scale at 12,000, and, no, breaking it up would not work.
If you've said what you needed to be said, then the chapter length, be it short or long, is perfect.