word count
Dear Shadow Ferret,
Your question is a good one, and one few early novelists and writers fail to consider. Diarrhea of the mouth is known in first-timers, who are shocked when no one wants to read their entire epic. And it can go the other way--an acquaintance told me she'd written a "mystery novel of 6,000 words."
The rule of thumb for published novels is 200-250 words per page. In manuscript format, a full double-spaced page with one-inch margins using Courier New is 250 words.
Mainstream commercial fiction novels are 300-350 pages.
Thrillers are more, usually around 100,000 to 120,000 words. This is a general rule of thumb too, but thriller/mystery/suspense writers often go 120k and pare to 100k or 110k in revision. These are the books you find in the "literature and fiction" section at Barnes and Noble.
If you hobble over to the mystery section, the books grow thinner (in general; James Lee Burke writes bigger books.) Romance? Harlequins are 50,000 to 55,000. I know a romance writer who puts out 3-4 a year on contract. There again, Norah Robert's books are bigger but her word-count per year may be the same as the romance writer.
You're writing Fantasy. I am not a fantasy writer, and have read few. My opinion is many fantasy books are way way way too long. I'm talking those over 200k. They just are not tightly written. I don't want to offend anyone and i'm not elitist about it--it's just an ignorant impression. I have read some wonderful fantasy over the years and enjoyed the ride. Heck, I even read Daniel Steel in a pinch in Mexico and had fun enough to read a couple more at home.
Yeah, write enough words to tell the story. But you're smart to be aware of what's going on in the business. Pages cost money to print. People like more pages for more money...if it's a good read.
You can test the numbers by typing out a page of a novel that interests you and see how many words per page, times total number of pages. Mass market and trade paperbacks, vs hardback differ in spacing, margins, hence words per page. This is fun to do when you're procrastinating the day's assigned writing.