Nielsen is launching Twitter TV Ratings, the first measure of the total activity and reach of TV-related conversation on Twitter—to help identify who's really engaging in real time and to better target ads.
The new ratings will measure activity—the number of people tweeting about television programs, and reach—the number of people who actually view those tweets.
(Read more: Facebook vs. Twitter: How they differ)
This new measure comes just days after Twitter released its public S-1 filing, showing fast revenue growth, but a lack of profitability. This new ratings system could help Twitter grow its revenue in one key area: partnerships with traditional media companies, which is an area that Twitter said in its S-1 filing has promising growth prospects.
Just last week Twitter announced major TV partnerships with CBS and the NFL. Both content providers will offer clips coordinated to what's airing on TV, along with ads. They will also pay Twitter to promote their content.
Why the focus on TV? The number of people talking about Twitter on TV has grown dramatically to 19 million in the second quarter of 2013, up 24 percent on year. The number of Tweets about TV has grown even more—up 38 percent on year at 263 million.
Nielsen said the Twitter TV audience for an average episode is 50 times larger than the number of authors generating tweets. For instance, if there are 2,000 people sending Tweets about a televising show, the average number of people viewing those Tweets is around 100,000 people. What does that mean? Major free advertising for TV shows.
Here's the thing: Tons of Twitter activity doesn't make for the most watched shows. Despite the fact that CBS' "The Big Bang Theory" and "NCIS" regularly draw more than 20 million viewers and are two of the top-rated shows on TV, they don't break into the list of the top 10 most Tweeted about shows on Twitter.
The most Tweeted about show, by far, during the final week in September, was the finale of AMC's "Breaking Bad." Though it broke certain records and drew 10.3 million viewers, that's a far cry from the kind of viewership broadcast shows draw. What that means is the audience for mainstream TV and Twitter's core tweeters about TV isn't exactly the same.
(Read more: How 'Breaking Bad' broke records)
The other clear message is that, which is no surprise, shows that must be watched live draw a much bigger Twitter conversation.
The second to fifth most Tweeted about shows for the week ended Sept. 29 are:
It's too soon to say how many media companies—or advertisers—will pay for the Nielsen ratings. Until that becomes clear we'll have to wait to see how they use that info and whether it drives more Twitter ad purchases.
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—By CNBC's Julia Boorstin. Follow her on Twitter: @JBoorstin.