<P> It is estimated that the population of the world reached one billion for the first time in 1804 . It would be another 123 years before it reached two billion in 1927 , but it took only 33 years to rise by another billion people , reaching three billion in 1960 . Thereafter , the global population reached four billion in 1974 , five billion in 1987 , six billion in 1999 and , by some estimates , seven billion in October 2011 with other estimates being in March 2012 . It is projected to reach eight billion by 2024 -- 2030 . According to current projections , the world 's population is likely to reach around nine billion by 2035 -- 2050 , with alternative scenarios ranging from a low of 7.4 billion to a high of more than 10.6 billion . Projected figures vary depending on underlying statistical assumptions and which variables are manipulated in projection calculations , especially the fertility variable . Long - range predictions to 2150 range from a population decline to 3.2 billion in the ' low scenario ' , to ' high scenarios ' of 24.8 billion . One scenario predicted a massive increase to 256 billion by 2150 , assuming fertility remains at 1995 levels . </P>
<P> It is estimated that the population of the world reached one billion for the first time in 1804 . It would be another 123 years before it reached two billion in 1927 , but it took only 33 years to rise by another billion people , reaching three billion in 1960 . Thereafter , the global population reached four billion in 1974 , five billion in 1987 , six billion in 1999 and , by some estimates , seven billion in October 2011 with other estimates being in March 2012 . It is projected to reach eight billion by 2024 -- 2030 . According to current projections , the world 's population is likely to reach around nine billion by 2035 -- 2050 , with alternative scenarios ranging from a low of 7.4 billion to a high of more than 10.6 billion . Projected figures vary depending on underlying statistical assumptions and which variables are manipulated in projection calculations , especially the fertility variable . Long - range predictions to 2150 range from a population decline to 3.2 billion in the ' low scenario ' , to ' high scenarios ' of 24.8 billion . One scenario predicted a massive increase to 256 billion by 2150 , assuming fertility remains at 1995 levels . </P>
approximately on which year the world population reached the first billion mark
approximately on which year the world population reached the first billion mark
1804
1804