The Super Bowl is undoubtedly the biggest American television event of every single year. Case in point: 19 of the 20 most-watched television shows of all time in the United States are Super Bowl broadcasts, with the series finale of M*A*S*H being the only non-Super Bowl telecast to crack the top 20.
Per Nielsen, the leader in American viewership statistics, last year's Super Bowl LI between the Patriots and Falcons drew an average of 111.3 million viewers in America. While that's more than a third of the U.S. population, that number is actually down from the prior year's Super Bowl 50. That Broncos-Panthers matchup drew 111.9 million, but that too was down from the prior year's matchup.
Super Bowl XLIX, which pitted the Patriots against the then-defending champion Seahawks, was the most-watched Super Bowl and most-watched television program of all time with a whopping 114.4 million American viewers.
There's reason to believe this year's Super Bowl viewership will be smaller than last year's, as the NFL's television ratings have been down across the board this season as the league has dealt with a number of image issues. Overall ratings dropped roughly 10% this season, a dip that hasn't excluded the playoffs–both the AFC and NFC Championship Games saw a decrease in year-over-year viewership, even with the AFC's Jaguars-Patriots matchup going down to the wire.
While the Super Bowl is the undisputed king of American television, it is not among the most watched sporting events globally. The World Cup final easily outdraws the Super Bowl globally, as more than 1 billion people tuned in to watch Germany beat Argentina in the 2014 final in Brazil.