Having just posted the latest chapter of my story on Facebook, it occurred to me that it was, in fact, a short chapter. Around 700 words, which is pretty short.
I went looking into "how long is a chapter," and found--lo and behold--that there's no magical minimal number involved. Chapters are, as it is pointed out, as long as the scene needs to be. Theoretically, you could have a chapter of one word...which would be weird, but you could do it if it was something like "Screams."
So far, my current story (unfinished) is 31000 words deep. Still not sure how long it will be, but we'll get there. I can't see the end yet, but I know we're making pace toward it. I didn't expect this chapter to be so short--but there it is, a quickie. Hey, if it moves the story and, hooks the reader, then you're doing it right.