Every television program receives a Nielsen rating, numbers in percentage form that show how many people watched that show. The ratings are provided by a firm called the A.C. Nielsen Company.
The company puts electronic boxes on about 1,170 TV sets around the country. These boxes register what channel each set was tuned to when it was on, and how long that channel remained on.
The 1,170 homes that are studied by the Nielsen Company are made up of the same mix of people that the whole population is made up of. So when a show gets a rating of, let’s say, 25, it means that 25 percent of the homes with a Nielsen box watched that show. People who work in television then figure that about 25 percent of all the homes in America with television watched that show.
The highest rated show of all time was the last episode of Roots, which first aired in 1977. The program received a rating of 51, which means that about 37 million TV sets in America were tuned in to that program!