Newbie Question #8

8. How do you decide how long a book should be?

I stop when I get to the end of the story.

But I suspect this is actually a question about industry standards, so here's what they are, according to the Nebula Awards:

Novel: a work of 40,000 words or more*
Novella: a work of at least 17,500 words but under 40,000 words
Novelette: a work of at least 7,500 words but under 17,500 words
Short story: a work of under 7,500 words

I should note that for anyone other than the Nebula judges 40,000 words is act...