Flash Fiction - 100 - 1,000 words
Short Story - 1,000 to 7,500 words
Novellette - 7,500 - 20,000 words
Novella - 20,000 - 50,000 words
Novel - 50,000 - 110,000 words
This is only a standard list to go by. Most markets will list their word count requirements in their market listing. Many markets will also vary slightly as to what they consider acceptable word counts for each. For example, some markets consider a novel to be no less then 70,000 words. Some markets might consider flash fiction no longer then 800 words. Be sure to research your market thoroughly and double check your word counts before you submit.