Most people I’ve talked to said that one should not think too much about word count at the beginning of writing. One should write what one wants. Of course there’s come a time when you’ll need to think about which audience your book is for, so you can have a rough idea how long your book should be. Though in my humble opinion, any author more or less knows for which audience he’s writing. Example, a gore horror story will not be good for middle grade, and the author must know that at the outset of writing. Or at least I hope he does.
Anyway, there still remains the crucial point. How long should be my novel? Assuming you know your target audience, here are lampposts to keep in mind.