How to Compute Earned-Run Average

 

Rule 10.22(e) states:

To compute pitcher's earned-run average, multiply the total earned runs charged against his pitching by 9, and divide the result by the total number of innings he pitched.  NOTE:  Earned-run average shall be calculated on the basis of total innings pitched including fractional innings.  EXAMPLE:  9 1/3 innings pitched and 3 earned runs is an earned run average of 2.89 (3 ER time 9 divided by 9 1/3 equals 2.89).

This rule is referenced by the notes to game 116 of the 2003 season.

These rules are quoted directly from the Major League Official Baseball Rules, which “govern the playing of baseball games by professional teams of the American League of Professional Baseball Clubs, the National League of Professional Baseball Clubs, and the leagues which are members of the National Association of Professional Baseball Leagues."