If you’re looking to do some number crunching and figure out how to calculate ERA you’ve come to the right place!
ERA or earned run average, is another way of saying “what a pitcher gives up per nine innings that he pitches.” With that being said, this is not to be confused with what EXACTLY crosses the plate every nine innings a hurler takes the hill. Keep in mind that unearned runs, which are runs that score with the benefit of a fielding error, are NOT added into the ERA calculation/formula. It should also be noted that when betting on games, this along with W.H.I.P. are the two most important ways that we’re going to grade a pitcher when we’re predicting the outcomes of baseball games.
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Add up a pitchers innings. An inning is three outs. If you see 6.1 or 6.2 that means 6.33 or 6.67 innings. Unlike some other baseball stats, we don’t round up when we’re talking about ERA.
Now add up all the earned runs the pitcher gave up during the innings he’s pitched. For arguments sake, lets say he gave up 3 earned runs.
Now multiply the earned runs by 9.
Now divide by the total innings pitched.
Example: A pitcher goes 5 innings and gives up 3 earned runs. We take the earned runs x 9 which gives us 27. We then divide this by the innings pitched 27 divided by 5 = 5.40.
In case you’re wondering what the good, bad and the ugly are ERA-wise in the big leagues it could be said that:
An earned run average of 2.00 or lower is an ace and a very sharp pitcher. Anything 3.00 or under is ROCK solid. An ERA of 3.00 to 3.50 is GOOD. Conversely, 4.00 to 5.00 is average and anything above 5.00 a guy is probably struggling to stay in the bigs and is getting hit pretty hard.
Related article: How to Calculate Batting Average