I understand that "her ne kadar" can mean "although / even though"  but can anyone provide any information as to why it´s used in this way? 

When I read it, i´m thinking "each how much?"

is it used commonly?

Here is my theory:

When her and ne comes together "her" starts to act differently. It functions like "ever" in the "what ever"

Her ne yaparsan yap, beni durduramazsın. What ever you do, you cant stop me.

It continues to function in the same way in "her ne kadar" unlike English.. A literal translation would be like this: "how much ever". But such an expression unfortunately doesnt exist in English