My wife says a 6 is sort of a Small/Medium, I think it is a larger Medium but still Medium. I know that is confusing. I am going to list a Jean Pants and Jacket matching set later and the Jacket lays exactly the same as this one, but the one I am going to list soon says XL, And I would put it at a Big Medium/ Large, So this is all I can say, This jacket says 6, I am guessing it would be a Medium/Large. Hope that helps, Sorry.
A size 6 in most stores is a baggy Medium and a fitting small I know this because I'm 5 4 and 125lb and I normally fit into a size 6 comfortably but I am 18 I hope I helped? A size 6 can be a little baggy like in H&M and Forever21 it's baggy.