I don't know what the usual rule is, but 3000 to 7000 words for a chapter seems about average on this site.
I also found that the feedback I got from posting here gave me more insight into how to end a chapter, when to extend a scene and when to shorten it, how long to make a paragraph, and other important stuff.
My advice is to post a chapter at a time here on this forum and take feedback here before posting to the library. It's very tricky, sometimes impossible, to make those changes later once you've posted to the library.