Summary:
China and India have the world's two largest populations, according to the CIA World Factbook.

Full article:
(CNN) -- The world's population is about to reach 7 billion on Monday, according to the United Nations. More than a third of the globe's people are in two countries. China and India account for more than 1 billion people each. Both have at least three times as many people as the United States, which has the world's third-largest population at a little more than 300 million. Visualize 7 billion at once . Indonesia and Brazil round out the top five, according to the most recent estimates from the CIA World Factbook. Twelve countries in the world have more than 100 million people. Eight of them are Asian countries. The other four are the U.S., Brazil, Nigeria and Mexico. At the bottom of the list is Pitcairn Islands, with an estimated 48 people. The British territory is in the south Pacific. More Comparisons: Which countries are perceived to be the most corrupt? Which country has the smallest gender gap? Where is the Internet most popular? Where are the undernourished? Where do people live the longest? Which countries have the most vacation days? Who requires the most education? Who's got the highest (and lowest) unemployment rates?