At 7.1 billion people, and 148 million km^2 of land area (or 36 billion acres) that is just over 5 of land surface area per living human soul. So what does that mean theoretically? It means that if the every person was given 5 acres of land and all the associated rights that they could make it work. But the monkey math continues, there is probably 40% of our planet that cannot be expected to produce, such as high mountains, deserts, and far North regions. So that would put it at something like 3 acres of useful land, I have got to get to work, more monkey math later!