A few questions about middle grade/young adult

[Southern_girl29]

I've started working on something new. I'm not sure if it's middle grade or young adult. I did a google search, and it seems like it might be young adult because of the age of the character and the subject matter. The MC is 14, and it's sort of a thriller/mystery. Anyway, what makes young adult and middle grade different from each other?

What is the typical word count on a young adult? Middle grade? How long are the chapters?

Thanks in advance. I'm super excited about this.

[Evaine]

Go to the library. Pull a few books out at random, and you'll soon see an average page count for the books, as well as details about chapter length etc.
You don't say what the subject matter is, so only you can decide whether it's YA or MG.