If my mom s paternal grandmother was full blooded Hungarian what percentage would I be?

Since your mother's paternal grandmother is 100% Hungarian, that makes your maternal grandfather half Hungarian, your mom 25% (or 1/4) Hungarian, which would make you 1/8 Hungarian (or 12.5%).

Hungarian is a nationality (a passport)..and an ethnicity (a culture). Here in the UK we would label ourselfs half Hungarian if one of our parents was from Hungary, we dont go to quarters one eighths etc.. Your an American with a Hungarian grandmother (or Hungarian ancestry, pecentages get ridiculous, most Hungarians will have non Hungarian ancestors just like the rest of the world, people have intermarried.

Because of its location primarily on a flat plain, Hungary has been overrun by invaders for centuries. When the Ottoman empire invaded in the 1500s, they killed or carried off many of the Hungarians who lived there, particularly in the western part of the country. The Catholic Hapsburgs, who rules that area, invited Catholic settlers to move into the good farmland in western Hungary in exchange for providing military support if the Ottoman Turks returned. So there was a large influx of Croatians from the South and Germans from southern Germany, along with Poles and Slovaks, into Hungary. They learned Hungarian, intermarried with whatever Hungarians remained in the area, and became the Hungarian people. Few Europeans are "pure" anything; they'll all become mixed due to wars, invasions and migrations.

Assuming no other Hungarian blood, 1/8

"full Blooded Hungarian, if there were such a thing, your Your Mothers Father would be 1/2; Your Mother would be 1/4 and your would be 1/8.

It depends on if you mean genetically or ethnically. Ethnically you would be 1/8 Hungarian, because you have eight great-grandparents, and one of them was Hungarian. Genetically, there is no way to tell, because the exact makeup of genes that is passed on is not equal from all of your ancestors. Maybe your mom didn't give you any of the Hungarian genes, or maybe she gave you an abnormally high amount of them. If you have a kid you will give them a mix of genes from your mom's side and your dad's side, but there is no telling how that will be split. You could give them 70% genes from your dad and only 30% genes from your mom for example. There are services that will test your DNA and try to determine what percentage of it came from which region of the world, but that is a new thing that is far from perfect.

You are American with a family story, you need to research and prove what you have been told, even if you find it to be true ( unlikely) because of the nature of the country and wider Austrian Hungarian Empire you are still American with Hungarian ancestry

The convention many people use, and many object to, is that you are half of what each parent was. Once you get the convention, the rest is just dividing by 2:

Mom's paternal grandmother = 1/1

Mom's dad = 1/2

Mom = 1/4

You = 1/8

If you are an American citizen, you are "an American with Hungarian ancestry" or an American of Hungarian descent."

One-eight.