I found it here.
I claims to you need at least 2 acres to support a family of four on a mixed diet of grains, veggies, proteins, etc. It is pretty discouraging when you think I just put our 2- 12 ft by 5 ft garden in last night. Not only was it tons of work. It hardly would make a dent in supplying what we need if there wasn't a grocery store 5miles away.