Basketball is all about efficiency. Maximizing points scored and minimizing points allowed on each possession is more important than overall totals. Offensive and defensive efficiency are adjusted for pace, calculating points scored and allowed on a per-possession basis. To make the numbers easy to digest, they are reported per 100 possessions so they look similar to points-per-game figures. Both ratings are still considered box score statistics as they rely purely on box score statistics. While the formulas are simple, there is an estimation requirement as the number of possessions must be calculated from box score data.
The number of points a team scores per 100 possessions. To calculate the number of total number of possessions for exact team you need use this formula:
field goals attempted – offensive rebounds + turnovers + (0.4 x free throws attempted) = total number of possessions for the season
This works because a possession can end only in one of three ways: an attempted field goal, a turnover or a free throw, with an offensive rebound negating additional field goal attempts.
Divide the team’s total points scored for the season by the possessions you calculated in Step 1. For example, 938 total points scored divided by 998 total possessions gives your team 0.94 points scored per possession. Numbers above 1.0 are generally considered good.
Convert the offensive PPP number to an efficiency rating by simply multipling by 100. So 0.94 points scored per possession becomes an offensive efficiency rating of 94.
Use the formula:
field goals attempted – offensive rebounds + turnovers + (0.4 x free throws attempted) = total number of possessions for the season to calculate total team possessions
Divide the total number of points allowed by your team by the possession total you calculated in Step 1. For example, 1009 total points allowed divided by 998 total possessions gives your team 1.01 points allowed per possession. The opposite is true for defensive PPP: Above 1.0 is bad; below 1.0 is considered good.
Convert defensive points per possession to a defensive efficiency rating by multiplying by 100. So 1.01 points allowed per possession becomes a defensive efficiency rating of 101.