A pitcher’s ERA, or earned run average, is a statistic used to calculate how many runs a pitcher gives up, on average, in the course of a full game pitched. The lower a pitcher’s ERA, the better. A softball pitcher’s ERA is calculated with almost exactly the same formula used to calculate a baseball pitcher’s ERA; the only difference is that the softball formula takes into account a shorter standard game (seven innings) than the typical nine-inning baseball game.
Research the number of earned runs a given softball pitcher has given up during any particular time period. Make sure to count earned runs only—runs scored as the result of another player’s error don’t count toward a pitcher’s ERA.
Add up the number of innings pitched during the same period of time. Make sure to include partial innings in fraction form (for example, the total number of innings pitched in the early part of the season might be 15 1/3).
Divide the number of runs earned by the number of innings pitched. This gives you the pitcher’s earned run average per inning pitched. If you want the ERA per game played, you’re not done yet.
Multiply the result from Step 3 by 7, the typical number of innings in a softball game. The resulting number is your softball pitcher’s ERA per game.
Because runs scored with the help of errors don't count on your ERA, the statistic offers a fair measurement of a pitcher's value. It also helps you compare pitchers on two different teams when one squad is poor defensively.