The majority of experts think that 3,000–5,000 words each chapter is a decent starting point. As a result, 12–27 chapters for a YA novel would be a reasonable starting point. From there, you may narrow it down even further by reading similar works in the genre you're writing in. For example, if you were writing a dystopian novel, you might find out that other novels in this genre usually only have 20 chapters. Of course, nothing here says you have to stick to these numbers. You can write whatever length book you want as long as it has enough chapters to be considered a novel. Most readers expect a young adult novel to have between 15 and 20 chapters. If your book doesn't cover enough ground in that time span, then it might not be long enough. On the other hand, if it goes on too long, then it's likely to feel like a chore to read instead of a fun adventure. As with most things in life, there is no right answer. What matters is that you follow your heart and write what you want to write without worrying about whether or not others expect you to write a certain way.