Worried about the future of some ABC TV shows? Take a look at the chart below to see their season ranking, averages to date, and their grade in the all-important 18-49 demographic.

There’s lots of information that the networks take into consideration when cancelling or renewing a TV series but the ratings are the biggest factor. (You can see if your favorites have already been renewed or cancelled by visiting our ABC 2011-12 show page.)

These charts incorporate final ratings data through Thursday, May 30, 2012.

Original ratings data ©The Nielsen Company. All rights reserved.

A couple of things to remember:
The averages included in these charts are based on the final numbers, not the fast affiliate ratings that are reported the morning after a show airs. These final numbers become available one to three days later (depending on holidays or weekends). The charts are updated as we get the new data.

Whether we like it or not, the demo numbers are what’s most important to the networks because that’s what’s important to advertisers. That’s how the networks measure success. Advertisers will pay more money for ad time on a show with a higher demo rating than one with more overall viewers. For example, Castle has more viewers than Grey’s Anatomy but an ad on Grey’s costs 30% more ($203,078 vs. $121,914).

Demo numbers are reported by Nielsen using the 10th decimal place (2.1, for example). In these charts, we’re including the rounded demo average as well as the average in 100ths (2.14, for example) in parenthesis so you can get a better idea of how the number’s been affected by the latest episode’s rating.

The letter grades are relative and are based on the individual network’s overall performance in either the scripted or non-scripted categories. The networks all have very different gauges for success. A hit show on The CW would get quickly cancelled on CBS. Our system for coming up with letter grades isn’t perfect but it should still give you an idea of where the shows stand when compared to others on the same network.

*The letter grades for TV series that run on Friday and Saturday nights are weighted a little differently to compensate for them airing on little-watched nights.

What do you think? How are your favorites doing? Are any of them in danger of being cancelled or sure to to be renewed?