Earned run average (ERA) is one of the most significant statistics in the game of baseball. It is a measure of a pitcher’s performance, based on runs allowed per 9 innings pitched. The lower the number, the better a pitcher has performed (and vice versa). Earned run average can be affected by ballpark size and altitude (particularly Coors Field in Denver), team defense, and the offense facing the pitcher.
Perhaps while watching a baseball game on television, you may have seen a number under the earned run average category and wondered about how that number was calculated. Well, finding this number is very simple, and I have outlined this process in 4 easy steps. In order to find this number, you will need a baseball card or a newspaper sports section, and perhaps a calculator for this exercise.
Look for earned runs. These are runs scored by the other team without assistance from the defense (such as an error). On the back of a baseball card or in the sports section of a newspaper, for example, you'll find this number under the abbreviation "ER".
It should be noted that some baseball cards will list both runs (usually unearned runs and abbreviated "R") and earned runs.
Multiply earned runs by 9 (as there are 9 innings in a regulation baseball game).
Look for innings pitched. This number can be found under the abbreviation "IP".
Note: At times, you will likely see this number listed as .1 and .2. However, it should be read in this instance as 1/3 and 2/3 (not 1/10 and 2/10).
Divide your answer from step 2 (ER x 9) by innings pitched, and then round your final answer to the nearest hundredth.
There are instances when a pitcher's earned run average will be infinite and abbreviated as "INF" in the stat sheet. This occurs when a pitcher (usually a relief pitcher who comes into the game to face one or two batters) gives up one or more earned runs without recording an out.