What is ERA in Baseball?

what is era in baseball

ERA stands for “earned run average,” and Henry Chadwick, an English-American sportswriter, statistician, and the “Father of Baseball,” created it. He was also instrumental in other game parts like the box score, batting average, and abbreviating a strikeout with the letter K. ERA is an important stat in baseball because it, in theory, shows how many runs per every nine innings pitched a pitcher gives up to their opponent.


So, how does ERA exactly work in baseball? What is the formula to calculate a pitcher’s earned run average? What happens if a pitcher leaves a game with runners still on base? Is it good to have a high or low ERA in baseball? Can you have a zero ERA in baseball?


Here is the complete breakdown to what ERA is in baseball.


How Does ERA Work?

how does era work

An earned run is any run scored as the direct result of a pitch rather than a fielding error or another factor. Conversely, an unearned run occurs during a mistake by another play, like a throwing error.


A pitcher’s main objective is to prevent the other team’s hitters from earning runs. A pitcher’s ERA represents the average number of runs they allow in a nine-inning game, so it is a pretty important measure for how well they achieve their objective.


So, at its most basic, an ERA is a pitching statistic that calculates how many earned runs a pitcher allows for every nine innings pitched. It gives a pretty accurate “ballpark figure,” so to speak, for how well a pitcher is performing throughout the season.


What is the Formula to Calculate ERA?

What is the Formula to Calculate ERA

ERA calculation is pretty simple. The formula for calculating ERA is:
(total number of earned runs allowed ÷ total number of innings pitched) x 9


This number gives you the average number of earned runs allowed per inning. ERAs are two decimal places and averages over a season or a career for a pitcher, depending on what you want to review.


So, for example, let’s look at a pitcher who has pitched 100 innings in a season. In those 100 innings, they’ve allowed 50 total runs. Of those 50 runs, only 40 of the runs were earned, and 10 were unearned runs. To calculate this pitcher’s ERA, you would divide 40 by 100 and then multiply by 9. This ERA comes out to a 3.60 for that pitcher.


What Happens if a Pitcher Leaves the Game with Men on Base?

does era factor if a pitcher leaves runner on base who then score

It is important to note that if a pitcher exits a game with runners on base, any runs earned by those runners still count against their ERA since they pitched to those runners and allowed them to get on base.


Is a High or Low ERA Better in Baseball?

Is a High or Low ERA Better in Baseball

A pitcher’s main objective is to prevent the other team’s hitters from earning runs. A lower ERA means that the pitcher has allowed fewer earned runs. Therefore, a low ERA is a better score than a high ERA.


In 21st century baseball, an ERA below 4.00 is considered good, and anything below 3.00 is great. An ERA below 2.00 is rare and signifies an exceptional pitcher. Anything above 5.00 is terrible, and generally, pitchers with that ERA either pitch during blow-out games or get sent to the minor leagues.


Who Had some Great ERA’s in their Career?

Who Had some Great ERA's in their Career

Ed Walsh, who played for seven seasons between 1906–1914, holds the lowest career ERA ever with an ERA of 1.79. Another notable pitcher was Bob Gibson, with an ERA of 2.91 over his seventeen-year career with the St. Louis Cardinals. He achieved a 1.12 ERA in his best season in 1968.


Dazzy Vance — who was known for his fastball and was the only pitcher to lead the National League in strikeouts for seven consecutive seasons — had an ERA of 2.16 during his best season in 1924.


Pedro Martinez of the Red Sox and eight-time All-Star is a more modern example of a pitcher with an outstanding ERA. He had a career ERA of 2.93 and a 1.74 ERA in his best season in 2000. Martinez’s 2.93 was only the sixth-lowest ERA for a pitcher who had pitched at least 2,500 innings.


Who Has the Lowest ERA Ever?

Who Has the Lowest ERA Ever

Tim Keefe holds the record for the lowest-ever one-season ERA in baseball history with a score of 0.86 while he played for the National League Troy Trojans in 1880.


Dutch Leonard, a left-handed pitcher who had an ERA below 1.00 in a single season, had an ERA of 0.96 while playing in the American League in 1914.


How is ERA Different for a Starter vs. a Reliever?

measuring era for starters vs relievers

The primary difference between a starter and a reliever is how many innings they pitch during a game. For example, a starter might only throw six innings one day a week. That means the pitcher needs to pace themselves to last six innings, so they might not throw as hard or pitch to contact to get batters out quickly.


On the other hand, a reliever might pitch six innings in a week, but they do that over six games. That means a reliever only has to pitch one inning during a baseball game, which means they can throw harder against hitters since it’s more of a sprint than a marathon in pitcher terms. However, a reliever who comes in during one inning might give up many runs, which would make their ERA look out of whack for that game compared to a starting pitcher.


Can You Have a Zero ERA in Baseball?

Can You Have a Zero ERA in Baseball

You might be surprised to learn that earned runs account for over 90% of runs in baseball. Unearned runs are relatively rare. This earned run metric results in ERA scores being higher than you might initially think.


Players can have a zero ERA listed, but this is not usually accurately representing their skill. Zero ERAs are also sometimes called undefined or infinite ERAs.


Zero ERAs are usually reported at the beginning of a season before there are statistics to report on complete games. If a pitcher allows one or more earned runs without retiring a batter, they will technically have a zero ERA since they did not record any outs. However, a pitcher has never sustained an ERA of zero for an entire season.


Conclusion: What is ERA in Baseball?

In summary, ERA is a great way to evaluate a pitcher’s effectiveness in limiting how many earn runs they give up over nine innings. For example, the ERA stat line is a better metric instead of how many wins a pitcher got. However, if you look for the best stat line for pitchers, baseball WHIP might be the best metric since that measures how many walks and hits they give up per inning.


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