BballChart app is designed to give all of the normally kept offensive basketball statistics in one calculation. The formulas are listed below. Enter the data that you have in the required data section. Then click on Calculate. You may change a field and re-calculate with other values remaining the same. You may also click on Clear Values and reset all fields and results to initial value defaults. If you only want a certain calculation, you may enter only the data required to save time and energy.

How to calculate game score

Game Score = Points Scored + (0.4 x Field Goals) – (0.7 x Field Goal Attempts) – (0.4 x (Free Throw Attempts – Free Throws)) + (0.7 x Offensive Rebounds) + (0.3 x Defensive Rebounds) + Steals + (0.7 x Assists) + (0.7 x Blocks) – (0.4 x Personal Fouls) – Turnovers

Example

In a game, a player has made: 26 points, 6 field goals, 21 field goal attempts, 14 free throws, 21 free throw attempts, 1 offensive rebound, 4 defensive rebounds, 1 steal, 10 assists, 1 block, 1 personal foul, and 7 turnovers.
Game Score (GmSc) = 26 + (0.4 x 6) – (0.7 x 21) – (0.4 x (21 – 14)) + (0.7 x 1) + (0.3 x 4) + 1 + (0.7 x 10) + (0.7 x 1) – (0.4 x 1) – 7
Game Score (GmSc) = 26 + 2.4 – 14.7 – (0.4 x 7) + 0.7 + 1.2 + 1 + 7 + 0.7 – 0.4 – 7
Game Score (GmSc) = 26 + 2.4 – 14.7 – 2.8 + 0.7 + 1.2 + 1 + 7 + 0.7 – 0.4 – 7
Game Score (GmSc) = 14.1
Therefore, this player has a game score of 14.1.

More resources:

Wikipedia – John Hollinger Game Score
Boxscore Geeks – FAQ – What are “Wins Produced?” – Includes reference to the Game Score formula.
Glossary Entries on Game Score from Basketball-Reference.com and SportingCharts.com.
Statistical entries including GmSc all time leaders from Basketball-Reference.com,