The minimum amount of agricultural land necessary for sustainable food security, with a diversified diet similar to those of North America and Western Europe (hence including meat), is 0.5 of a hectare per person. This does not allow for any land degradation such as soil erosion, and it assumes adequate water supplies. Very few populous countries have more than an average of 0.25 of a hectare. It is realistic to suppose that the absolute minimum of arable land to support one person is a mere 0.07 of a hectare–and this assumes a largely vegetarian diet, no land degradation or water shortages, virtually no post-harvest waste, and farmers who know precisely when and how to plant, fertilize, irrigate, etc. From the FAO (the Food and Agriculture Organization of the United Nations (1993)
there's 15 billion acres of land, and this doesn't count the sea or ancillary resources like urban farming, i assume. just to keep anyone from taking this data in a malthusian direction. 1 billion americans (as they are now) is a nightmare