The population of the United States is only 4.3% of the world total, but its citizens hold nearly two fifths of the the world's total wealth.
United States . At 3.8 million square miles ( 9.8 million km2 ) and with over 324 million people , the United States is the world 's third - or fourth-largest country by total area , third-largest by land area , and the third-most populous . Though its population is only 4.3 % of the world total , Americans hold nearly 40 % of the total wealth in the world .