Super Bowl 51 drew a 48.8 overnight rating
Super Bowl 50, had a 49.0 rating.
Super Bowl 49, the game where Brady won his fourth Super Bowl ring against the Seattle Seahawks, had an overnight rating of 49.7, which is a record for overnight ratings
Interesting to see what this year's numbers are ...
Not exactly, you are looking at share number not the total audience #s while 45.3% of tv’s were tuned to last years super bowl it was the largest audienece in viewers with 172,000,000
February 2, 2014 XLVIII Fox 167,000,000 46.7
February 1, 2015 XLIX NBC 168,000,000 47.5
February 7, 2016 50 CBS 167,000,000 46.6
February 5, 2017 LI Fox 172,000,000 45.3
Additionally the the last four super bowl games are the 4 highest rated tv programs ever, and the final episode of mash is the only program in the top 20 rated tv programs of all time that was not a super bowl game.