One birth every.................................. 8 seconds One death every.................................. 12 seconds One international migrant (net) every............ 36 seconds Net gain of one person every..................... 14 seconds
The U.S. population clock is based on the national population estimates. The U.S. Census Bureau produces national population estimates annually using the latest available data on births, deaths, and international migration. Each year, we recalibrate the population clock when we release the new set of population estimates. For more information on the methodology for producing national estimates, see http://www.census.gov/popest/topics/methodology/2008-nat-meth.pdf [PDF].
Historical National Population Estimates [PDF - 81K]
Documentation for these projections.
[PDF] or