30.6( broadcast TV) + 16.9 (CNN.com) = 47.5 million...plus the other streaming services and the 250,000 to 1,900,000 on the Mall.

Reagan (81) 41.8 ( broadcast TV)   - Mall does NOT hold 7+ million
Obama (09) 37.7 ( broadcast TV)   - Mall + streaming over 9.8 million?

A good argument can be made that the Total Watching was the largest.

""the largest audience to ever witness an inauguration — period — both in person and around the globe,""