It’s not so simple a question, after all.
Genre norms do provide some clues for your novel’s word count. But when you’re writing a novel, you need more than that.
You need to know what your target readers expect. When they pick up your book, will they be disappointed if the spine is less than an inch thick?
Or are they likely to want something they can finish more quickly?
How many words are in a novel that most of your ideal readers are looking for? And where do you get this information?