The US Census Bureau has calculated that the milestone will have been reached by 1.24am this morning - only 40 years after the population of the planet stood at half that figure.
Although the growth of the human race is now slowing, the world population has risen by one billion in the past 12 years, an increase that threatens disaster for much of the planet.
The bureau's estimatecomes about three months before the date set by the United Nations - 12 October.
At the end of the last Ice Age there were about 10,000 people on earth. The one billion mark was reached at the beginning of the 19th century, and the three billion figure 150 years later. The global population expands by 78 million a year.
The rate of growth is now slowing because of better access to contraception and changing attitudes. It takes 70 years for a country's population to stabilise after it achieves a balanced fertility rate.
The global population will reach 8.9 billion in 2050 and will not level off until about 2200, when there will be roughly 11 billion people on the planet, according to the UN's population division.Reuse content