Every reader has a preference on what she likes to read, but what about the length?
What do you think about the length of a story? Some stories take longer than others to tell. Shouldn’t that be the determining factor? Sometimes it isn’t.
I don’t know any guideline that says this amount of conflict is that amount of story. Is there a limit to what I can show in a flash fiction piece? In a novel? I’m sure, but each author treats things differently. You can overstay your welcome in a scene, or you can gloss over too much and enter the dreaded realm of ‘telling’.
All of us have our own ideas about what length the story should be. Isn’t the adage to always leave them wanting more? Not a lot more, surely, but something has to keep those pages turning.
Ransom Noble 
I think that every story has its own length already determined. It is the writer behind the story you have to worry about. When I read ‘the Lovely Bones’ (I can’t remember who wrote that) I got done with it and said to my wife, that was a short story that was turned into a short novel. She agreed with me. It wasn’t that it was a bad novel, but I think it would have been a better short story.
I agree that the length depends on the stories. I enjoy different types of lengths. Some shorter novels are great and yet I also like to read epic fantasy novels (which are notorious for length).
I thought Lovely Bones was fine as a novel. My introduction to it was a small bit performed in drama for speech. But then in college had to read the book for a class and the author spoke on campus. She was interesting but not prolific.