High school basketball’s RPI explained
By: Andrew Woods
Posted on:
RPI, explained
Since the 2023-2024 season, the OHSAA has used the Rating Percentage Index to seed teams for the basketball tournament. However, a version of the Rating Percentage Index is nothing new to Ohio high school sports. Since 1971, Ohio has used a similar system, Harbin points, to determine which teams qualify for the playoffs in football. This article will explain how the relatively new RPI system works and how it is used. It will also compare and contrast it with the Harbin points system that high school football fans have known about for decades.
How is RPI calculated?
The RPI formula is:
40% win percentage x 40% opponent’s win percentage x 20% opponents’ opponent’s win percentage.
How is RPI win percentage calculated?
Similarly to the Harbin points system, each opponent is worth a certain number of points depending on their size. Below are how many points an opponent from each division is worth. Note that teams must be members of their state athletics association for their games to count for RPI points. For example, games against Ross County Christian Academy and New Hope Christian Academy will not be counted for RPI purposes because those schools are not sanctioned by the OHSAA.
- Division I – 2 points
- Division II – 1.85 points
- Division III – 1.70 points
- Division IV and Out of State – 1.55 points
- Division V – 1.40 points
- Division VI – 1.25 points
- Division VII – 1.10 points
Also like the Harbin points system, losses are not worth any points toward a team’s adjusted win percentage. However, unlike Harbin points, points earned are divided by the number of games a team has played times the number of points that team’s division is worth.
How does first-level win percentage work in practice?
As an example of how first-level win percentage works, I will use the Athens Lady Bulldogs’ first five games of the season. The results of those games were:
Loss at Hillsboro
Win at Warren
Win at Marietta
Loss at Circleville
Win at River Valley
(The scores from those games do not matter for RPI purposes.)
The Hillsboro and Circleville losses are not worth any RPI points, so those can be excluded from the calculation. Warren and Marietta are Division III teams, both worth 1.7 points, while River Valley is a Division V team, worth 1.4 points. That adds up to 4.8 points.
For the divisor, the number of games Athens played (5) is multiplied by Athens’ division value. Athens is a Division III team, so for the Lady Bulldogs’ divisor, you would multiply 5 (the number of games Athens played) times 1.7, which equals a divisor of 8.5.
With the dividend of 4.8 points and the divisor of 8.5, you can now calculate Athens’ RPI win percentage by dividing 4.8 by 8.5, which gives you a win percentage of 0.564 or 56.4%.
How are opponents’ win percentage and opponents’ opponent’s win percentage calculated?
The opponents’ win percentage is simply the average of all a team’s opponents’ RPI win percentages, excluding all games played against the team whose RPI is being calculated. For example, when calculating Athens’ opponents’ win percentage, all games against Athens are excluded for RPI purposes.
In addition, note that unlike Harbin points, all opponents (not just opponents a team beat) are included when calculating opponents’ RPI.
However, the biggest difference between Harbin points and RPI is that RPI uses opponents’ opponent’s win percentage, while Harbin points do not use opponents’ opponent’s wins except for tiebreakers.
Opponents’ opponent’s win percentage is calculated similarly to opponents’ win percentage. Opponents’ opponent’s win percentage is simply the average RPI win percentage of all of a teams’ opponents’ opponent’s, excluding all games played against the opponents of the team whose RPI is being calculated. For example, when calculating Athens’ opponents’ opponent’s win percentage, all games involving Hillsboro, Warren, Marietta and River Valley, as well as any other opponents Athens played throughout the season, are excluded from the opponents’ opponent’s win percentage calculation.
How is RPI used?
Unlike Harbin points, but like years past where coaches determined seeding for the basketball tournament, all teams that opt in to playoffs will play at least one postseason game.
In addition to seeding, RPI is also used to determine district assignments. For example, in last season’s Division VII district tournament, as the first overall seed, Waterford had the right to determine whether their bracket’s winner would play as the Southeast 2 or the Southeast 1 champion. The Wildcats chose to play as the Southeast 2 champions, which worked well for the Wildcats because the Southeast 2 winner was slotted against the comparatively weaker winner of the Central 1 district, rather than the winner of the East 1 district. After the district assignments are determined, teams are placed in their bracket according to their RPI ranking. For example, last season, Trimble had the fifth-highest RPI among all the Division VII teams in the Southeast District, so the Tomcats played as the #5 seed in the tournament.
As the tournament draws for this season’s basketball tournament come closer, understanding RPI will continue to be important for players, coachesand fans across the Hardwood Heroes coverage area and beyond.