For fiction: if your work is below 100 words it’s microfiction (superhard, I love it! For an excellent example check out Objects of Desire by Adam O’Fallon Price ), below a 1,000 words it’s flash fiction, below 30,000 words it’s a short story, below 50,000 a novella, above 50,000 it’s a novel (a fictional book). These ranges vary, but this is a good gauge. I will have a separate post with where to publish, based on length :)
The length of a novel will depend on the genre, YA (young adult) is 50,000-80,000, any other fiction genre between 80,000 and 100, 000 with the exception of historical and science fiction which can get up to 120,000. Look up your specific genre once you find out or feel free to ask.
Does this matter? Yes. If you are a best selling author you may do as you please, but if you are a first time author avoid any possible red flags, a superlong or short work being one of them.
That said, my first book is a YA novel around 70,000 words long, but I have at least 180,000 words in the garbage. We’ll talk about that (carving a book out of your draft) soon :) Meanwhile keep in mind that when you write your first draft you might want to be way over your word count, because a quarter to half of your draft will be pared down.
Thanks for reading ^_^