New York City-based sharing service Tumblr continues to grow at an incredible pace, hitting 20 billion posts on Monday night, doubling in size in just over 6 months.

Understated in its response to the milestone, the Tumblr team posted a tweet to notify its followers:

Sure enough, if you visit the Tumblr About page, the service currently hosts 20,060,823,987 posts and is approaching 50 million blogs (49,725,785 at the time of writing).

Screen Shot 2012 03 28 at 14.28.59 520x247 Tumblr hits 20 billion posts, nears 50 million hosted blogs

On May 1, 2011, Tumblr included more than 5 billion total posts and over 17.5 million total blogs, hitting 10 billion in September. This meant that the service doubled its total output in just four months and doubled it again in a little over six — impressive.

At the beginning of the year, Tumblr founder and CEO David Karp announced at the Digitial Life Design (DLD) conference that the company was serving 120 million people and 15 billion pageviews every month.

Speaking about how Tumblr differs from traditional “editorial” services like WordPress, Karp quoted figures from website traffic measuring company Quantcast, not directly referencing internal figures from its own analytics.

Referencing the social aspect of the service, Karp said that the average Tumblr blog is re-blogged nine times, helping to distribute user content to wider audiences via RSS, Twitter, Facebook and other social sharing services, that can be synchronised with the blogging platform.

Screen Shot 2012 01 23 at 08.46.54 520x324 Tumblr hits 20 billion posts, nears 50 million hosted blogs

Tumblr’s main audience comes from the U.S, with 45% of visitors (249 million) to its networks coming from America alone. Brazil makes up a large part also with 49 million visits, with the UK accounting for 34 million visits. To date, Tumblr has seen more 560 million people view content on its networks.

We’re such big fans of Tumblr’s growth, we’ve even started a weekly column called Tumblr Tuesday, where every Tuesday we celebrate our love of Tumblr by interviewing the mastermind behind the blog.

Moving forward, Tumblr’s CEO said that Tumblr will go “all in” and expand on the East Coast, bringing in talent from all over the country to work in New York. The Tumblr founder says he doesn’t believe it’s easy for new users to immediately use the service and start interacting with Tumblr blogs, the team is aiming to make it easier for people to find, digest and share content in the future.