How to Calculate ERA
By Loot, MLB Handicapper, Lootmeister.com
ERA is the telltale stat of any pitcher. A pitcher with an ugly losing record can stay in the league on the basis of having a solid ERA. At the end of the day, a big part of determining the worth of a pitcher is to determine how many runs he allows. And that is basically at the root of ERA--a stat that breaks down how many earned runs a pitcher allows for every 9 innings.
ERA accounts only for runs where the pitcher is responsible--hence the name “earned run average.” In other words, a pitcher is not penalized for runs caused by reasons other than his pitching--like errors or runs scored by base-runners who got on base with a different pitcher on the mound.
It could also be said that ERA does not account for the total number of runs that cross the plate when the pitcher is on the mound. It is only having to do with runs where he is responsible. While the WHIP stat (walks + hits divided by innings pitched) has picked up some steam as a reliable meter to judge a pitcher’s effectiveness, ERA is still the only stat that directly addresses exactly how many actual runs a pitcher allows per 9 innings.
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To calculate ERA, take the total number of earned runs and multiply that by 9 and then divide that figure by the total number of innings pitched. Often times there will be portions of innings, namely a third and two-thirds of an inning. A third is worth .33, while two-thirds is .67. In other words, 5 and a third innings would be 5.33, while 5 and two-thirds innings would be 5.67.
So, getting back to the computation of ERA, you take the total amount of earned runs allowed, multiply by 9 and divide by the total innings pitched. Let’s do an example. A pitcher goes 7 innings and allows 3 earned runs. Take 3 (earned runs) and multiply by 9, which gives you 27. Divide 27 by 7 and you get 3.857. You round that 7 up and you get 3.86 as an ERA.
Let’s do a computation for an entire season. Let’s say a starting pitcher allows 87 runs in 212 innings pitched. Multiply 87 by 9 and you get 783. Divide that by the total innings pitched, which is 212. 783 divided by 212 and you have a respectable ERA of 3.69.
Depending on the type of era the baseball is taking place, an effective ERA can have different standards. In a dead-ball era or a period of extreme offensive productivity, what is considered a good ERA can vary. In the 70’s and 80’s, a pitcher with an ERA over 4.00 was considered shaky. But during the “juice era” when Bonds, McGwire and Sosa were banging out tape measure round trippers, an ERA of 4.00 was actually considered pretty good. (For more info on this topic, see our article: What is a Good ERA? What is a Bad ERA?)
Generally speaking, any starting pitcher with an ERA in the area of 2.00 is considered an ace. Any pitcher with an ERA near 3.00 is doing good and his career in the major leagues is stable. He is a pitcher teams would like to have. If a pitcher is under 4, he is a very serviceable pitcher. A starting pitcher with an ERA a little over 4.00 is OK, but the closer he gets to 5.00, the closer he is to being out of the league.
Closers have tighter standards. Pitching only one inning, they are expected to have a low earned run average. But ERA isn’t the best stat for relievers, as they usually inherit base-runners. “Blown saves” is the more reliable stat, as a reliever can have a low ERA without really getting the job done, which is to squash rallies. Still, a solid closer should have an ERA in the 2.00-3.00 range, with the best relievers sometimes well under 2.00. In 1990, closer-extraordinaire Dennis Eckersley only allowed 5 earned runs all season in 73.33 innings, for an ERA of 0.61. In 1968, starting pitcher Bob Gibson threw an incredible 304.67 innings, only giving up a scant 38 earned runs for a record-setting ERA of 1.12.
If you enjoyed this article, you might also be interested in checking out our piece on What is WHIP in Baseball?.