No, wait. It doesn't just "matter." Word count can completely dash your chances of representation. Sound a little drastic?
I just read a query for a hard SF manuscript. There I was, intrigued by the synopsis and all juiced up to request sample chapters. My eyes must have skipped right over the bit that said, "Complete at 240,000 words" as I went back to sighing over what looks like a fabulous breeze outside my window. Thankfully I snapped back to reality enough to read that sentence again, and a rejection letter soon followed.
Read this and read it good: 240,000 is obscene. Ob. scene. for a first novel.
You might think, "But Amy, what about authors like JK Rowling and Tad Williams? They've published gazillion-word novels that have done fabulously!" And you'd be right. But those authors earned the right to such lengthiness. They started out, like everyone else, with novels of a more palatable length. If they weren't above the rules, bucko, neither are you.
So what should you be shooting for? A good average is around 90,000 words. 45 - 60,000 if you're writing a YA novel. A thriller better reach 85k. Anything too much over 120,000 words and you're likely fast-tracked to a form rejection. Keep it in mind.
Happy writing, y'all.
Necessary Qualifier: This is simply the mind of one agency. Some agents, see Nathan Bransford's post on Word Count, have a far more...lenient approach. That's cool. He, of course, has a fair point. In the end, if the work is stellar keep-my-eyes-glued-to-the-page-for-all-240 THOUSAND-words- stellar, than YEA, I'm in. But that has only happened once in Linn's 15 year track record.
And she battled the work down to 180k.
Case and point.