The surface of our planet is made up of 70% water and 30% land. In total, the Earth contains approximately 57.47 million square miles of land. Of this, 20% is covered in snow, 20% is mountainous, 20% is dry land, 30% is fertile, and 10% has no topsoil:
http://hypertextbook.com/facts/2001/DanielChen.shtml
Using the above figures, I calculate that there are currently about 17.241 million square miles of fertile land on our planet– which translates as roughly 11.034 billion acres of food-sustaining land.
As of 2008, the world human population on Earth was almost 6.7 billion individuals:
http://www.google.com/publicdata?ds=wb-wdi&met=sp_pop_totl&tdim=true&dl=en&hl=en&q=current+world+population
Now, let us go over some hypotheticals, shall we?
If all 6.7 billion individuals on Earth were to evenly distribute, then live upon the roughly 11.034 billion acres of fertile land available on our planet, every single man, woman and child in the world would have approximately 1.647 acres of their very own self-sustaining property to live upon!
