It depends where you're from my friend. And even then, each individual case is subject to a great deal of variance.
It is often easier to go by the physical characteristics of your parents and grand parents, as well as their surnames. For example, my family clans are all from areas heavily settled by the Norse and a few family names are Scandinavian derivatives. Likewise we are full of red heads and blondes, with the deepest hair colour being caramel and no cases of brown eyes going back at least 4 generations. That in addition to us all being 6'1 + (myself being 6'7 and my uncle being 7'2) tends to incline me towards a Nordic pagan belief system. Which ever way you go, there is bound to be at least some of each in your line so I wouldn't worry about it too much. Hell, even Icelanders have a considerable Celtic admixture.
Though if you really want fine tuned answers, any reasonable DNA test will provide you with the exact make up of your heritage.