This is taken from The Vegetarian Myth by Lierre Kieth

A ten acre mid-atlantic farm of perennial polycoluture would produce

3000 eggs

1000 broilers

80 stewing hens

2000 pounds beef

2500 pounds pork

100 turkeys

50 rabits

She comes up with about 7 million calories per year, which is another issue but I did the math on this and came up with a similar estimate so I'll stick with this for now. Assuming we need 2500-3000 calories per day, this would be around 900k-1 million calories per year, so this lot would feed about 7 people. Keith actually says 9 people, but this on 2000 calories a day, which I don't think is a good estimate. This is assuming zero-carb of course but, I'm looking for a very general estimate so the specifics do not matter here yet.

I think she has farmland acreage estimates in her book but I'm going to use this government site -

http://www.ers.usda.gov/StateFacts/US.htmThe US has 2.26 billion acres of which 41 percent of which is farmland or 922 million acres. This is broken down to the following

Harvested cropland - 310 million acres

Woodland - 75 million

Pastureland - 410 million

If we used all the pastureland and harvested cropland for the above (720 million acres) and using the figure of .7 people fed per acre, this alone would be able to feed 500 million people. Obviously, there are a lot of assumptions here, namely that all the cropland would be able to produce equally and that Kieth's .7 people per acre figure is correct. Even if we take half of this figure, the US is nearly fully self-sustainable.