I had one of these living outside my childhood home in the Southern US too. It was probably about that big. Orb-weavers are awesome. Look them up. Most, if not all, are completely non-poisonous.
We have a few varieties of these lovelies here in the Florida/Alabama region. I always loved finding one of their webs when I was a kid. The spiders look like they're crafted by jewelers and the webs are always enormous glittering cathedrals of silk.
Sadly, their numbers have taken a hit due to a boom in the spider wasp population. The wolf spiders are declining as well. :(