I did some napkin calculations once. Try it too. Take available land surface (wikipedia or somewhere else) and divide it by population. Then compute the side of

I did some napkin calculations once. Try it too. Take available land surface (wikipedia or somewhere else) and divide it by population. Then compute the side of the square this surface represents. Take out living space and roads and rivers and lakes and mountains waste land and garbage land and... well, just do the division and you'll see what i mean.