Facebook Inc. said on Tuesday that it has 2 billion regular users, another milestone in its growth from a college curiosity to the world's largest social media network.

Chief Executive Mark Zuckerberg disclosed the number to his followers in a Facebook post. "It's an honor to be on this journey with you," he wrote.

The user base is bigger than the population of any single country and of six of the seven continents. It represents more than a quarter of the world's 7.5 billion people.