No, not THAT. This is a (mostly) family blog.
What I mean is, how long is your novel?
It's a simple question but not necessarily a simple answer. Sure, you can use the word count feature in your favorite work processing program to tell you. I think that's just part of the answer, though. The other part is genre expectations.
Let's say you want to write a sweeping epic. That's probably going to be something in the fantasy genre. Think Robert Jordan, just with things actually happening on the pages. A book like this could be 150,000 to 200,000 words, and that's OK because readers have become conditioned to expect that.
If you're writing a mystery novel, however, and your word count is encroaching on 200,000, you'll need to do some serious editing. I'm not saying you can't write a super-long mystery; it's just exceedingly rare to see. Readers expect to enjoy a book where the protagonist gets sucked into events that unfold at an appropriate pace.
My own current work in progress got me thinking about this. My past mysteries have checked in around 72,000-75,000 words. That's not by design. I don't see the word count odometer roll over to 72,000 and think, "whoa, I'd better wrap this up!" It just works out that way. The current WIP just went over 72,000 and I still have three chapters (and a few important events) to go. My guess is the first draft will check in around 80,000, then get trimmed in editing.
It sounds like I'm obsessed with word counts. I'm not. I'm more concerned with pacing. The word count is a sign post, a mile marker. Keep your eyes on it as you write, and understand its significance, but don't be a slave to it. Don't shorten or lengthen your story just because you think it needs to be within a certain word count range. Genre expectations are one thing. Good pacing is another.
Happy writing. Smile at the mile markers as you zoom past them.
* The title of this post is a line from "Big Ten-Inch Record," originally recorded by Bull Moose Jackson, and most popularly covered by Aerosmith.