In the United States the “replacement level” for births is 2.1. On average a woman needs to give birth to 2.1 living children to sustain the residential population of the United States.
In the United States we presently have a population of about 314 million. If you had no immigration or emigration, each woman would need to give birth to 2.1 children to sustain the population. The two children represents the eventual replacement of the mother and father. The .1 children represents the reality that some women die before giving birth and some never have children.
According to the U.S. Division of Vital Statistics the replacement level in the United States has dropped to 1.88 in 2012. The population in the United States continues to increase, however, through immigration. If immigration were to end, the United States would have a declining population.
According to the CIA Factbook, 94 of 224 countries (42%) listed have a replacement level birth rate below 2.0. Those countries include the United Kingdom, Netherlands, Norway, Australia, Finland, Denmark, Sweden, Belgium, Russia, Canada, China, Spain, Bulgaria, Hungary, Greece, Poland, Ukraine, Hong Kong, Taiwan and Singapore.
The countries with the most births per woman are Niger, Mali, Somalia, Uganda, Zambia, Afghanistan, South Sudan, Congo, Nigeria, Ethiopia, and Malawi. These countries have 5 or more births per woman.