It's a much asked question: How long should my work be? In all honesty, I don't know. But, I've been doing some research, and I can tell you the generally agreed on word count targets.
By story type (fiction)
Short story: under 7.5k words
Novelette: usually somewhere between 7.5k and 17.5k
Novella: usually somewhere between 17.5k and 40k
Novels are a bit more complicated.
The bare minimum would be 40k, though NaNoWriMo classifies it as over 50k. 80k to 90k is a good target to aim for, leaving room to add/remove things in future edits. On the other end of the scale, anything over 110k is considered an epic.
Then there's the specific genres.
Romance: 85k to 100k
Horror: 80k to 100k
Mystery: 65k to 90k
Fantasy: 100k is pretty ideal, but different sub-genres can vary, anywhere from 80k to 120k. Some editors will even accept up to 180k, but it would have to be really good.
By target age
Picture books: 350 to 600 words
Early readers: under 2.5k
Kids' chapter books: 6k to 10k
'Tweens': 30k to 45k
Young adult: 45k to 80k
Adult: 80k to 90k
If you're looking to get into the publishing world, make sure to check out what the publishers are looking for. If they want a 115k high fantasy, you won't get very far by submitting a 75k YA romance.
It should also be noted that exceptions can be made for sequels. For example, the first Harry Potter book is just over 77k, and it progressively increases as the series goes on, the last one nearing 200k.
Also, it's always easier to get rid of stuff, than to flesh it out more, so I'd reccomend to aim higher than you expect the final draft to be, so you can get rid of all the filler stuff.
I was about half-way through writing this when I found an awesome blog post that says a lot of this, and more. It's in the external link, if you want to find out more.
What would your WIP be classified under?
