It's a question hairstylists and reliable friends are often asked: "Do you think I can pull off short hair?"
To try it, position a pencil or pen under your chin horizontally and then place a ruler under your ear vertically. Take your measurement from the intersection of the pencil and ruler. Less than 2.25" and you'd look amazing with short hair; anything more, and long locks will be the most flattering choice for you.
See how it works on Michelle Williams and Kim Kardashian: