Genre Fiction Word Count Guidelines
If you're a new or newish author who has just finished writing a fabulous novel and are ready to shop that sucker to agents, you may want to take something into consideration before you start querying: Word count. This is a much bigger deal than many first time authors realize, and the wrong word count can you get your query a form rejection before your hook is even read. You see, each genre has its own word count guideline and you really need to follow it if you want an agent to work with you. A lot of authors think more is more, but sometimes more is too much. Seriously. Big deal, this is. Guidelines below, you read; famous author you may become if you get it right.
Please note that these guidelines are not written in stone. Some agents will take on anyone with a word count under 150k, some will not. But if you take a look at publisher's websites, a lot of them stipulate that your MS has to be under 90k, which means your agent would need to be clever to get your 150k onto their presses.
Also note that there are subcategories that also have their own word counts that may differ from what I've listed here. These are just a general rule of thumb. That said you really should be sure your novel has been trimmed of all the useless fluff that slows a book down and unnecessarily plumps your book up. Agents and readers both want a riveting fast read and 200k is unlikely to fall into that category.
Mainstream Contemporary Romance: 80,000 to 109,000
This is not just a romance novel, but also has something else going on to keep the reader's interest. Anything between 80k and 90k is going to work fine. Anything between 90k and 100k is probably fine if you've got a strong manuscript. Anything between 100k and 109k probably needs to be pretty fab if you want an agent to read it without panicking that a publisher is going to call it an epic and say its too long. Anything over 110k is probably going to get a form rejection unless you're already Stephen King or JK Rowling. Big books are expensive to produce and publishers will probably not want to risk big losses on a new author unless you're uber special.
Other types of romance:
Generally between 80k and 90k is what's going to get your query read. If you've got a historical you're shopping, these are longer and fall between 90k and 100k. Obviously there are also the "long" versions, which can tack another 10k onto the word count but this is really not recommended for first time authors. If you've got a shorter middle grade novel, see a few pegs down the list.
Fantasy and SciFi
These genre books run long and you can actually aim for a minimum 80k and go up to 120k (you epic writer, you!) if the work is really stellar. I don't read this genre myself because of all the wordiness they tend to employ, but hey, some people like dat.
Middle Grade Fiction
This is actually about the age of the intended audience and not the quality of your writing! This is the pre-teen age group. You know, not quite a teen, not quite a tot. Or whatever. These books should not be uber long, as the attention spans of these readers tends not to support such things. 20k to 40k or so will do, depending on the specific age you're gearing it toward.
YA (young adult)
If you write something they like, young adults have a much better attention span than middle graders, so you've got some leeway here. Anything between 50k and 75k is probably fine.
These can be epic, but you should probably aim for somewhere between 50k and 80k.