A former student who now lives in Hawaii wrote to me and asked me about the word lengths of short stories, novellas and novels.
The last short story I wrote when I was at Goddard College ran 9,000 words. LONG. My instuctor, the novelist Kathryn Davis, never talked about word lengths. She was more interested in the art of the story, and in craft, and figured a story would run as long or short as it needed to. I, of course, had no idea that it would be considered too long, though I did end up placing it in a literary journal. Short stories run typically 1,500 - 3,000 words, with some as short as 250 words. Amy Hempel has some very short stories--a couple of paragraphs--and there are anthologies called Flash Fiction and Sudden Fiction with these very short shorts. I also always say, whatever works...works. If you are writing a story that is running long, let it. Let it be what it is going to be. From writing that long short story, I came to realize I was more interested in book length pieces.
A novella, even more difficult to place than a short story, said the wonderful short story writer Antonya Nelson when she came on my show, and tend to run around 20,000 words to 40,000 words give or take a few thou.
Novels usually begin at 50,000 words and go to 100,000. For first novels, to go longer than that, I hear, is taking your life into your own hands. At 50,000 words, picture Brave New World, picture Animal Farm.
But again, if it works, it works, no matter the length.