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How To Calculate Earned Run Average

By Edited Nov 13, 2013 0 0

Baseball more than any other sport is a game of numbers. These statistics allow fans to make comparisons amongst players and even allows for comparisons between current players and all-time greats. Just as a batting average is a great measure of hitter effectiveness, a pitcher's earned run average (ERA) is a great gauge of a pitcher's likelihood of success against an opposing team. The method of how to calculate earned run average is an easy formula that will help your decision making in fantasy baseball leagues drafts, sports betting or acting as statistician for your neighborhood little league team.

The formula:

(Earned Runs x 9) / Innings Pitched

This simple formula does it all. Given a pitcher's earned runs, you multiply by 9 and then divide by the total number of innings pitched. Let us use a real example and view Nolan Ryan's stats for the 1987 season:

Earned Runs = 65

**It is common to represent partial innings as .1 or .2 to symbolize the number of outs, but when the math is performed these should be converted to proper decimals. In this case, Ryan pitched 211 complete innings and 2 outs which is 2/3 inning or .667 making his actual innings pitched 211.667. This will ensure an accurate calculation. Likewise, as another example, 15.1 innings would be 15.333 innings when properly factored.

Then using our formula:

(65 x 9) / 211.667 = 2.763 or 2.76

since ERA is always shown as rounded to two decimal places.

Ryan actually led the league in ERA in 1987 with 2.76. He also led the majors with 270Ks that year, but finished with an 8 –16 Record! The poor hitting Houston Astros gave his efforts little support. Even this poor win/loss record did not stop the Ryan Express from finishing in the Top 5 voting for the Cy Young Award that year. His ERA shows just how good he was, but received little help. This shows why ERA can help provide an explanation for a seemingly dismal season and to allow for better decision making.

Cy Young of the Boston Red Sox

If the Earned Runs are not given to you, or you are tallying for a game then just remember, the pitcher responsible for placing the runner on base gets saddled with the Earned Run if that baserunner scores – even if the responsible pitcher is no longer in the game. Also, if there is an error and runner(s) score, the number of Earned Runs should only be the number of runs that would have scored had the fielding been made cleanly.

If a runner pitches a shutout for a game or season, it is easy to see that his ERA is 0.00.

(0 ER x 9) / IP = 0.00. It doesn't matter how many innings pitched because if he never gave up a single earned run the numerator will always be zero and zero divided by ANY number is zero.

Many people get confused by a pitcher having allowed Earned Runs but without retiring a batter. For example, in his debut Wild Thing allows 3 runs on 6 walks and fails to retire a single batter before being yanked by his angry manager and shoved on a bus back to the bush leagues. His ERA?

(3 ERs x 9) / 0 IP = undefined

With a zero in the denominator, this result is undefined since a number can NEVER be divided by zero. However, from calculus days, this result as the denominator gets closer and closer to zero is infinity and normally the pitcher's ERA will be represented by the infinity symbol (∞).

Once you master earned run average, you can tackle hitting stats like calculating batting average and calculating slugging percentage, too. So grab your calculator and get to calculating! The baseball cards are on the shelf and the season is about to begin!



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