How do I check if player is 5 studs out from the edge of a part?

I know about magnitude and how to use it. I'm wondering if I could find the distance between the player and the outside of a part? Magnitude compares the distance between the centers of an object. If I wanted to see if the player is 5 studs outside of an object, I would have to create values for every different-sized part. Not to mention parts that aren't shaped like squares.