All told, Avatar's estimated admission count is 60.7 million thus far, or less than Titanic through the same point (47 days in). It's also less than half of Titanic's 128 million total estimated admissions. Emphasizing the impressiveness of Avatar, it took such recent blockbusters as The Lord of the Rings: The Return of the King, Spider-Man 2, The Passion of the Christ and Star Wars: Episode III - Revenge of the Sith their entire runs to reach around 60 million admissions.
Unfortunately, the industry does not track admissions, only dollars. Absent proper admissions tracking, estimated admissions are determined by dividing the grosses by the average ticket prices, but this method is certainly iffy and should not be seen as definitive. It's best used for recent releases that have complete box office records, but, even then, one may know the national average ticket price but not the average for an individual movie. The audiences vary demographically and regionally for each movie, which means different average ticket prices. What's more, for a picture like Avatar, the method does not address leveling the playing field for the possible deterrent of higher ticket prices, how the 3D presentations impact 2D attendance or how 3D currently has far fewer theaters than past 2D blockbusters.
However, it's better to have an approximation than to have nothing. Only the money may matter to Hollywood, but attendance is important from an audience and cultural perspective. The disparity between Avatar and Titanic is so huge according to this method, that it is safe to say that Titanic sold a boatload more tickets.
Pointing out the estimated admissions in no way diminishes the box office achievement of Avatar. The purpose is to add perspective. There is no doubt that Avatar is a phenomenon in its own right with its own unique set of circumstances and that it stands as one of the greatest box office runs of all time.