Graduation

Hey girls, so I know its prom season however I'm not going just because it's not really my kind of scene. Anyways, I've been thinking about grad and I noticed that some people in previous years had long dresses, like a prom dress style. I also noticed that some girls had shorter dresses that end just above the knee. The difference seems really significant based on the formality.

I was just wondering, how do you know what kind of dress to get?

Thanks:)