Every second, on average, around 6,000 tweets are tweeted on Twitter (visualize them here), which corresponds to over 350,000 tweets sent per minute, 500 million tweets per day and around 200 billion tweets per year. The chart below shows the number of tweets per day throughout Twitter's history:
The first tweet was sent on March 21, 2006 by Jack Dorsey, the creator of Twitter. It took over three years, until the end of May 2009, to reach the billionth tweet. Today, it takes less than two days for one billion tweets to be sent.
In Twitter's short history, we went from 5,000 tweets per day in 2007  to 500,000,000 tweets per day in 2013, which represents a six orders of magnitude increase. The intermediate steps were 300,000 tweets per day in 2008,  2.5 million tweets per day in 2009,  35 million tweets per day in 2010,  200 million tweets per day in 2011,  and 340 million tweets per day when Twitter celebrated its sixth year on March 21, 2012. 
Number of Tweets growth rate
From Twitter's launch in 2006 and until 2009, the volume of tweets grew at increasingly high rates, approaching a 1,400% gain in daily volume year to year  and around 1,000% gain in yearly volume.
By mid 2010 the rate of growth started to cool down, sliding eventually below 100% gain in yearly volume in 2012. Today, the volume of tweets is growing at around 30% per year in our estimation.
- Not all seconds are equal on Twitter: while around 6,000 tweets are sent in an average second today, over twenty times that amount (143,199 tweets) have been tweeted in a single record-breaking second on August 3, 2013, when people in Japan were viewing and tweeting about the animated movie Castle in the Sky as it was being aired on TV. Four years earlier, when Michael Jackson died on June 25 of 2009, a mere 456 tweets per second had sufficed to set the all-time record at the time.
- What if we drew a dot on the map for each geo-tagged tweet sent from around the world? Twitter's "Visual Insight Manager" Miguel Rios did just that, and here is the result.
- One tweet that will be hard to pinpoint on a map is the first live tweet from space, sent in January of 2010 by Astronaut Timothy Creamer.
- The name for the social network was initially envisioned as "stat.us" but was changed to “Twttr” when the prototype was introduced in March of 2006 (see Jack Dorsey's original sketch of Twitter), to finally become "Twitter" as the service was launched publicly on July 15, 2006.
- Whether you are a regular tweeter or only just sent a single tweet in the past, your "body of work" is now part of the Library of Congress. Twitter has in fact agreed to provide the largest library in the world with every public tweet ever sent, and to continue to supply tweets to the Library's archive on an ongoing basis.
Current tweet estimates are delivered by Worldometers' RTS algorithm, which processes data elaborated through statistical analysis after being collected, among others, from the following sources:
- Raffi Krikorian - VP, Platform Engineering, Twitter Inc.
- Kevin Weil - former Tech lead of Twitter Analytics, Twitter Inc.
- Official Twitter Blog Network
- Dick Costolo - CEO, Twitter Inc.
- "#numbers." Twitter Official Blog. March 14, 2011.
- Weil, Kevin. (VP of Product for Revenue and former big data engineer, Twitter Inc.). "Measuring Tweets." Twitter Official Blog. February 22, 2010.
- Krikorian, Raffi. (VP, Platform Engineering, Twitter Inc.). "New Tweets per second record, and how!" Twitter Official Blog. August 16, 2013.
- Twitter Engineering. "200 million Tweets per day." Twitter Official Blog. June 30, 2011.
- "Twitter turns six." Twitter Official Blog. March 21, 2012.