China's population of 1.3 billion constitutes 19.19% of the world population of 6.7 billion.It is estimated that China's population will grow until 2030 and after that it will see a drop. On the other hand, India the 2nd most populated country whose population is 1.2 billion will be the most populous country by 2040 with expected population of 1.52 billion.
United States with the population of more than 313 million constitutes about 4.5% of the world population. It is said that among the industrialized countries, the population growth of USA is the highest. Japan, the 10th most populous country with the total population of 127 million, is seeing a fall in birth rates in recent times.