The Super Bowl is annually the most-watched television event, having pulled in more than 100 million viewers every year since 2010. And once the dust settles at NRG Stadium in Houston, and the ratings start to come in Monday morning, this Super Bowl should be no exception.

But what do those numbers really mean? FOX Sports Executive Vice President of Research, League Operations & Strategy Michael Mulvihill explains:

  • The first number to be released by Nielsen Media Research is the Metered Market Rating, which measures 56 major markets in the United States. This represents about 70 percent of the country and is an early indication of what the final number will be. Metered Market Ratings are available around 8:00 AM ET and are the first numbers we see.
  • The Fast Nationals measure every market in the country and provide demographic information, including age groups, gender and more. The Fast Nationals give us a rating and also the average viewership, allowing us to say how many people watched the event – in this case Super Bowl LI. Fast Nationals are usually released around 1:00 PM ET.
  • There is also another number that comes out throughout the course of the day, which does not provide an accurate viewership representation of our event – a Fast Affiliates number. The Fast Affiliates are used to measure primetime viewership only – from 8:00-11:00 PM on the East Coast and from 8:00–11:00 PM on the West Coast. Since the Super Bowl starts at 6:30 PM ET and 3:30 PM PT, the Fast Affiliates don’t give us the full picture. Fast Affiliates are usually released around 11:00 AM ET, and since they come out before the Fast Nationals, some outlets publish them. However, the Fast Affiliates do not reflect a true representation of the audience and are lower than the actual viewership.