I heard Stefan of the Peter Schiff Show mention when talking to someone claiming that humans were "burdensome" that the entire population would fit into the state of Texas, with a couple of acres.
http://en.wikipedia.org/wiki/Texas Area = 696 241 km2
http://en.wikipedia.org/wiki/World_population Population = 7.142 billion
at 247 odd acres per km2, = 171971527 acres
171971527 / 7142000000 = ~0.024 acres or ~97 m2
is my maths correct?