I'm not sure why I'm answering this, but
Land mass, miles^2 = 3,537,438
People (Est) = 300,000,000
Land per person = 3,537,438 / 300,000,000 = 0.0118 miles^2 / person
0.0118 miles^2 / person @ 5280 feet / mile = 328,727 feet^2 / person
328,727 feet^2 / person @ 1 acre / 43560 feet^2 =...