The first inaugurations of Presidents Ronald Reagan and Barack Obama were the only ones to exceed Joe Biden's in popularity among television viewers over the past 40 years.

The Nielsen company said that 33.8 million people watched Biden's inauguration over 17 television networks between 10 am and 4 pm last Wednesday.

Reagan's festivities in 1981 drew 41.8 million viewers, and Obam''s 2009 inaugural reached 37.8 million, Nielsen said.

Perhaps most important to a former president known to watch television ratings closely: Biden exceeded the 30.6 million who watched Donald Trump take office in 2017, Nielsen said.

CNN was the most popular network for inaugural viewers, Nielsen said. Meanwhile, Fox News' audience for Biden's oath of office and inaugural address was down 77 per cent from the network's viewership for Trump.