"...using Word with 10 pt. courrier type, double spaced, with one-inch margins, you will have approximately 25 lines per page with 10 wordsper line. So figure 250 words per page.
An average book is about 200 pages, so that's about 50,000 words. Chapters are usually about 15 or 20 pages. Just divide it up like that."
-- Writing Books
Basically, there are no definite rules on how many words makes a chapter, because it depends very much on the rhythm of writing. I think one can say "something between 1,500 to 5,000 words" - 5,000 word chapters are LONG. Relating to Nanowrimo, one can say a chapter should take 1-2 days, not more, nor less. The medium word count for a day is 1,667 words a day, to reach the 50,000 words a month goal, so 1,667-3,334 words for a chapter is good. Also, if you write a chapter in 1-2 days, you will end up with at least 15 chapters, 30 if you write short chapters - or more than 50,000 words. :-) That is an ok length for a book.
The publishers don't like the bricks of books, with more than 90,000 words, but they also don't like books that are as short as 50,000 words.
Ok, I'm just talking, to keep me from writing before midnight :-D It's quarter past 4 P.M.