Hint fiction <= 25 words
Dribble <= 50 words
Drabble <= 100 words
Flash fiction <= 1,000 words
Short story between 1,000 and 7,500 words
Novelette between 7,500 and 20,000 words
Novella between 20,000 and 50,000 words
Novel > 50,000 words
These are only guidelines but seem to be widely accepted.