How many users did Instagram have when Facebook acquired it in 2012?

Instagram had 30 million users when Facebook agreed to acquire it in 2012.

Instagram began as Burbn, a location-based check-in project created by Kevin Systrom and Mike Krieger. They refocused it around photo sharing and launched Instagram in October 2010. Its growth was rapid: it reached 1 million registered users by December 2010, 10 million by September 2011, and 30 million by April 2012.

Facebook announced the acquisition on April 9, 2012, for approximately $1 billion in cash and stock. The deal officially closed on September 6, after regulatory reviews. A common mix-up is the 50 million figure: Instagram reached roughly 50 million monthly active users later in April 2012, after the acquisition announcement.