Over a third of US adult Internet users have used Wikipedia, according to the Pew Internet and American Life Project.
The user-generated encylopedia claims over 5.3 million total entries, 1.6 million of them in English.
So who is using the site?
Half of those with at least a college degree have used Wikipedia, compared to 22% of those with a high school diploma. About half of current adult full- or part-time students have used the site, while 36% of the general online population have.
The site's demographics skew young. While 44% of those ages 18-29 use Wikipedia, just 29% of users ages 50 and older go there.
comScore Media Metrix says that the Wikipedia group of sites is one of the top 10 globally in terms of monthly traffic.
Hitwise also counts Wikipedia as one of the top 10 sites on the Web.
According to Pew, more Internet users visit Wikipedia on a typical day than buy something online, visit dating sites, make travel reservations, use chat rooms or participate in an online auction.