The U.S. population clock is based on a series of short-term projections for the resident population of the United States. This includes people whose usual residence is in the 50 states and the District of Columbia.
These projections do not include members of the Armed Forces overseas, their dependents, or other U.S. citizens residing outside the United States. The projections are based on a monthly series of population estimates starting with the April 1, 2010 resident population from the 2010 Census.
The World population clock is based on a series of projections that includes births and deaths, and end result (shown) is the total number of living humans on Earth.
According to a separate estimate by the United Nations Population Fund, world population reached 7 billion on October 31, 2011. In fact, the world population has experienced continuous growth since the end of the Great Famine and the Black Death in 1350, when it stood at around 370 million.