According to the Real-Time Statistics Project, some 500 million tweets are sent out each day, adding up to some 200 billion per year.
The key figure used to measure Twitter's success is the number of its monthly active users, which has remained at 320 million for the past two quarters. Twitter says the vast majority of these -- 254 million -- are outside the United States.
But chief executive Dorsey says another 500 million people use Twitter without logging in, and the company has launched an effort to draw more ad revenues from those visitors. Twitter also says one billion people each month view sites with embedded tweets, which further expands the reach of the platform.