Roughly 30.6 million people tuned in to watch the former real estate mogul as he was inaugurated as the 45th US president.
But despite claims he drew the biggest crowds in presidential history, Mr Obama actually had 19 per cent more viewers - 37.8 million people - watch his 2009 inauguration, according to Nielsen.
Nearly 28 million Americans watched Mr Trump's Afghanistan speech on Monday, 32 per cent fewer viewers than Mr Obama's in 2009.
Mr Trump regularly claimed during his election campaign that his events brought in the highest network ratings.
The largest demographic to watch his Afghanistan speech - 17 million people - was those aged 55 and older. Conversely, just two million people between 18 and 34 tuned in.
His first address to Congress on 28 February drew 47.7 million viewers, compared to Mr Obama's in 2009 which saw 52.4 million viewers tune in.
In his first televised White House interview, Mr Trump was asked why he spent his first day in office summoning reporters to talk about the size of the crowd at his January inauguration.
His then press secretary Sean Spicer told reporters that he drew "the largest audience ever to witness an inauguration, period, both in person and around the globe," despite overwhelming evidence to the contrary.
Mr Trump told ABC News: "Part of my whole victory was that the men and women of this country who have been forgotten, will never be forgotten again.
"Part of that is when they try and demean me unfairly, because we had a massive crowd of people. We had a crowd… I looked over that sea of people, and I said to myself, ‘wow’, and I’ve seen crowds before. Big, big crowds. That was some crowd."