According to a January story written by Jacopo Prisco for CNN, each year between 300 and 900 Super Bowl rings are produced, depending on the desires of team ownership. Those rings are, in turn, given to the list of people that the owner(s) have decided have earned it.
Of course, all of the players on the roster for the championship will receive a ring—this includes practice squad members, players on injured reserve, and those who were on the roster for the Super Bowl itself, regardless of when they joined the team and if they were active or not.