Monday evening’s debate was the most-viewed presidential debate in the history of such televised events. According to early Nielsen household TV ratings, at least 80 million people watched Hillary Clinton and Donald Trump go head-to-head for their first of three debates. Because those numbers do not include PBS, C-SPAN, or live-streaming options, the numbers will significantly rise when final viewership data becomes available, thereby breaking the 81 million viewership record set by the 1980 debate between Ronald Reagan and Jimmy Carter. The big 2016 numbers also dwarf those of the first Obama-Romney debate in 2012, which averaged 67 million viewers. Additionally, according to Nielsen data, Monday evening’s viewership stayed high throughout the entire 98-minute event, with no significant dropoff after the first hour.
SOURCE: The Daily Beast Cheat Sheet