1/3 the size of Obama would be 600,000. http://www.politifact.com/truth-o-meter/article/2017/jan/20/inaugural-crowd-sizes-ranked/ Barack Obama, 2013: 1 million Barack Obama, 2009: 1.8 million (generally considered a record for people on the National Mall) George W. Bush, 2005: 400,000 George W. Bush, 2001: 300,000 Bill Clinton, 1997: 250,000 Bill Clinton, 1993: 800,000 George H.W. Bush, 1989: 300,000 Ronald Reagan, 1985: 140,000 tickets sold, but record cold moved the swearing-in ceremony indoors Ronald Reagan, 1981: 10,000, according to the New York Times. This was the first year the ceremony was performed on the west side of the Capitol.
Obama lost nearly half his attendees for his second inauguration. 4 years seeing him in action. Clinton lost 550,000 of his 800,000. The three republicans grew their audience.
DJ Trump sounds like the 4th Beastie Boy. (Yes, I know Mix Master Mike is the 4th Beastie, I just didn't think you honkies would.)