Calculate a baseball player’s ERA or earned run average, by dividing the number of earned runs allowed by the number of innings pitched, and multiply by nine. ERA represents the average number of earned runs pitchers give up per nine-inning game and is the primary measure of a pitcher’s effectiveness.
- Add up the innings pitched
Add up all the innings that a pitcher has pitched, including partial innings. Because an inning has three outs, compute partial innings by converting one-third of an inning to .33 and two-thirds of an inning to .66.
- Add up the earned runs
Add up all the earned runs the pitcher gave up during the innings he pitched. An earned run is a run is a run that an official scorer has ruled to have resulted exclusively from actions by the batting team, such as hits and walks. Unearned runs are not included and are runs that result from errors by the defensive team.
- Calculate the ERA
To calculate the ERA, multiply the number of earned runs by nine, and then divide by the total innings pitched. An ERA below two is considered excellent, while an ERA around three is good, and anything above four is average.