Yesterday night, Facebook reached a milestone – 350 million registered users. That’s pretty impressive for a website which was started from a Harvard dorm room. Few moments ago, I was busy pressing my Sharp scientific calculator, calculating when Facebook will surpass the 1 billion mark if the social networking website continues its current exponential growth. The number I got was 1001 days or 2.74 years, which turned out to be on August 28, 2012, about 4 months away from the “end of the world” on December 21, 2012, according to the Mayans.

My calculation:

It took Facebook 77 days to gain 50 million users from 300 million on September 15, 2009 to 350 million on December 1, 2009. By dividing 50 million by 77 days, it gives me the answer 649,350. This simply means that on average, 650,000 people sign up for a Facebook account every day or 7.5 a second.

To reach the 1 billion mark, Facebook still needs 650 million people to join the social networking site. By dividing 650 million by 649,350, I get the answer 1001. This means that if Facebook continues to grow at such an impressive rate, then in 1001 days later or on August 28, 2012, the folks at Facebook will celebrate its 1 billion milestone on this day.

Yes, it may sound absurd to many of you guys as what I’ve calculated above is just a rough estimate and Facebook’s growth will start slowing down after its climax is over. However, if the Chinese government lifts the ban on Facebook (currently, it’s being blocked in China), I believe it’s still achievable by 2012 or 2013, all thanks to China’s relatively huge population. As of June 30 this year, the total number of China’s internet users reached 338 million representing a 13.4% increase from the end of 2008, according to a report by the China Internet Network Information Center (CNNIC), a government-affiliated Web research organization.

Till date, there are only about 1.65 billion active internet users in the world and it’s estimated that the global internet population will grow to 2.1 billion in 2012, potentially to 2.5 billion by 2015. For Facebook to achieve that mark, it would need to achieve nearly 50% penetration of Internet users in almost every country outside of China, if the Chinese authorities fail to unblock Facebook in China in the next 1 or 2 years.

Facebook continues to increasingly saturate some western markets and the number of users from Southeast Asia is rising rapidly. On the other hand, Friendster, which once dominated the region, has been slowly losing grip of their social network dominance.

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In Europe, there are about 100 million Facebook users, according to InsideFacebook. And the numbers are heading north, especially in Turkey, Italy and France. The United Kingdom is still the largest Facebook country in Europe, with 20.6 million monthly actives.

A Look Back at Several Crucial Milestones of Facebook’s Growth:

Dec. 1, 2009: 350 million users (77 days since last benchmark)
Sept. 15, 2009: 300 million users (62 days since last benchmark)
July 15, 2009: 250 million users (98 days since last benchmark)
April 8, 2009: 200 million users (91 days since last benchmark)
Jan. 7, 2009: 150 million users (134 days since last benchmark)
August 26, 2008: 100 million users

Frankly speaking, it’s quite hard to imagine what how a world with 1 billion Facebook users look like and I wonder how is the Californian-based company going to manage 1 billion people with only 900 employees, which is equivalent to 1 employee serving 1.1 million users. That’s insane! Of course, Facebook will continue to add more talented engineers into its current workforce in the near future.

Sources: Facebook blog posts, Gigaom and InsideFacebook.