Truth is every man, woman, & child in the whole world could have about 1 acres of land to themselves & it would all fit into a land mass the size of North America, with the rest of the world completely unoccupied.
Total land area of North America (including Central America and the Caribbean): 24,486,305 km² (6,050,697,738 acres)
Average population density of North America: 21.0 persons per square kilometer (11.77 acres per person)
Total population of Earth 6,553,289,000
Average population density of Earth: 44.0 persons per square kilometer (5.62 acres per person)
6,050,697,738 acres of North America / the total world population of 6,553,289,000 = 0.93.. acres per person (not families mind you, that would take up less land maas)
North America at http://en.wikipedia.org/wiki/North_America
Population Clock at http://www.census.gov/main/www/popclock.html