Obama inauguration TV viewership down by 17.2 million from 2009

U.S. President Barack Obama turns to look at the crowds gathered on the National Mall as he leaves the podium after his swearing-in ceremonies on the West front of the U.S Capitol in Washington, January 21, 2013.

LOS ANGELES (Reuters) - Some 20.6 million Americans watched President Barack Obama's inauguration ceremony and related events on television, according to ratings data on Wednesday. That's down sharply from his first inauguration in 2009.

TV ratings company Nielsen said 18 U.S. television networks and cable channels carried live coverage over about six hours of Monday's swearing-in ceremony, speech and parade in Washington.

Monday's TV audience was a drop of 17.2 million from 2009, when 37.8 million Americans - the highest number since Ronald Reagan's 1981 inauguration - watched Obama formally take office as the first black president in U.S. history.

The Nielsen figures did not measure viewers who watched Monday's daylong ceremonies online via live streaming on many TV channels, nor overseas audiences.

Second-term inaugurations of U.S. presidents have traditionally drawn smaller numbers of viewers than those for first terms.

Reagan's 1981 inauguration drew the biggest television audience of the past 44 years, attracting some 41.8 million U.S. viewers, according to Nielsen.

(Reporting By Jill Serjeant; Editing by Bill Trott)