The opening night of the Democratic National Convention drew more than 22 million viewers, a 20% larger audience than in 2004, according to Nielsen Media Research.
If you want even more detail on the numbers (and I know you do) check out this post on the very helpful blog, TV By The Numbers.
To keep all of these numbers in perspective, consider that 22 million is double the 10.7 million that watched ABC's broadcast of the April 16 Clinton-Obama debate in Pennsylvania and five to twenty times the audience size of the many debates broadcast in 2007.
On the other hand, 22 million is still a far cry from the 62 million that watched the first Bush-Kerry debate in 2004.
These numbers show us that while the conventions are the most watched political events so far this cycle, they are still not quite the voters-as-jury experience that we sometimes assume. The news coverage that excerpts speeches and convention "moments" reaches a far bigger cumulative audience. Those of us interested in measuring the impact of the debates need to allow time for Americans to view that coverage, absorb it and sleep on it for a few days.