The official college basketball Ratings Percentage Index (RPI) is calculated by the NCAA. That RPI can be found here.
There are two other generally accepted sources for the RPI, Sportsline.com: CBS Sports and RealTimeRPI.com, but their RPI calculations may not be the same as each other or the NCAA. Both CBS Sports and RealTimeRPI.com use the same generally accepted RPI formula as the NCAA to calculate the current RPI but as you will see below their results can differ.
As of this writing on November 23, 2008 at 10:15PM EST, SportsLine.com calculates the Top 5 RPI as follows.
| RPI Rank | Team | Wins | Losses | RPI | SOS Rank | SOS |
| 1 | Butler | 2 | 0 | 0.8542 | 7 | 0.8056 |
| 2 | Texas | 2 | 0 | 0.8125 | 19 | 0.75 |
| 3 | Evansville | 2 | 0 | 0.8125 | 20 | 0.75 |
| 4 | Wisconsin | 2 | 0 | 0.8125 | 22 | 0.75 |
| 5 | Virginia | 3 | 0 | 0.8125 | 21 | 0.75 |
RealTimeRPI.com calculates the Top 5 RPI as follows.
| RPI Rank | Team | Wins | Losses | RPI | SOS Rank | SOS |
| 1 | Virginia | 3 | 0 | 0.9464 | 1 | 0.9286 |
| 2 | Butler | 2 | 0 | 0.85 | 5 | 0.8 |
| 3 | Miami (FL) | 1 | 0 | 0.8125 | 20 | 0.75 |
| 4 | Texas | 2 | 0 | 0.8036 | 26 | 0.7381 |
| 5 | Michigan | 2 | 1 | 0.796 | 4 | 0.8049 |
CBS Sports does not publicize how often it updates the RPI but the results on it’s college basketball pages are updated in realtime. There is no reason with results in realtime that it is not calcuating the RPI in realtime too.
RealTimeRPI.com claims to update it’s RPI every 5 minutes. From the site, “We have a dedicated staff monitoring all college games/schedule and perform comprehensive analysis. All info is updated every 5 mins.” Not to take anything away from the “dedicated staff,” but I expect RealTimeRPI.com actually has a web-based application calculating and posting the RPI every five minutes.
How is the RPI calculated?
The RPI is a three part forumla with the three parts representing 25%-50%-25% of the total index. The three parts are:
1. Winning Percentage – 25%.
2. Strength of Schedule (SOS) – 50%. The SOS is readily available on a number of sites including SportsLine.com: CBS Sports and RealTimeRPI.com.
3. Opponents Strength of Schedule -25%.
RPI Links
The NCAA RPI can be found here.
The SportsLine.com: CBS Sports RPI can be found here.
The RealTimeRPI.com can be found here.
Originally Posted: November 23, 2008.
Update: May 20, 2011.