Six Billion Of Us Factmonster

World Population Milestones

1 billion in 18042 billion in 1927  (123 years later)3 billion in 1960  ( 33 years later)4 billion in 1974  ( 14 years later)5 billion in 1987  ( 13 years later)6 billion in 1999  ( 12 years later)

Source: United Nations Population Division