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A Beginner’s Guide to Baseball’s ERA Statistic

The game of baseball is full of statistics. In fact, there are over 100 statistics that are used in the MLB. And out of all those statistics, ERA is one that stands out most when discussing the effectiveness of a pitcher. However, understanding a pitcher’s ERA is not something that is intuitive. Lots of people wonder what this number means and how it’s utilized. What is ERA in baseball?

Pitcher in a pinstripe uniform standing on the mound in the rain with text that reads "A Beginner's Guide to Baseball's ERA Statistic"

ERA stands for “Earned Run Average”, which calculates how many earned runs a pitcher gives up over the course of a nine-inning game, on average. ERA is calculated by dividing the number of Earned Runs (ER) by the number of Innings Pitched (IP), multiplying by 9, then rounding to two decimal places.

ERA has been used since the 1870s and has become ingrained in baseball’s lingo. For the rest of this article, we’ll discuss what ERA is, how it’s calculated, and how it’s used by players and coaches.

What is ERA?

ERA is an acronym for “Earned Run Average” and it is one of the many statistics tracked in baseball. There are over 100 statistics in baseball, which are broken down into “standard statistics” and “advanced statistics”. ERA is considered a standard statistic.

ERA is a commonly used statistic to judge the effectiveness of pitchers because it measures how well pitchers prevent runs. It does so by calculating how many earned runs a pitcher will give up, on average, over a span of nine innings.

It is important to note that ERA looks at earned runs, not all runs. An earned run is another type of statistic that looks at how many runs were scored because of something the offense did. If the defense allows a run because of an error or a passed ball, it is considered an unearned run and it does not count towards a pitcher’s ERA.

There can be a lot of caveats on what is an earned run and what is an unearned run. In fact, scorekeepers routinely need to “reconstruct” an inning to determine if a run was earned or unearned. If you’re interested in learning more, read about what makes a run an earned run.

A common point of confusion around this statistic is whether a high ERA is better than a low ERA. Since ERA is an indicator of how many runs a pitcher allows, a lower ERA is considered better than a higher ERA. And while ERA is not the only statistic used to evaluate pitchers, coaches still prefer pitchers with a low ERA. Read more about why a low ERA is better than a high ERA.

How to Calculate ERA

Illustration showing how to calculate ERA in baseball

Now that we have a high-level understanding of what an ERA is, the next thing you’ll want to know is how to calculate a pitcher’s ERA. How is ERA determined in baseball?

ERA is determined by dividing the number of Earned Runs (ER) by the number of Innings Pitched (IP), multiplying that number by 9, and rounding to two decimal places. ERA indicates how many earned runs, on average, a pitcher allows over 9 innings.

Although 9 innings is the most widely accepted format for calculating ERA, there are some differences in this calculation that depend on your level of play. For example, youth baseball leagues, high school baseball, and softball.

For these leagues where the standard game is not a 9-inning game, you would calculate a pitcher’s ERA by dividing the number of earned runs by the number of innings pitched, and then multiply that number by the length of a standard game. So high school baseball and softball would both need to be multiplied by 7 because a standard game in those leagues generally lasts 7 innings.

The good news for fans is that ERA is relatively easy to calculate and the formula is easy to remember. If you’re interested in learning more, read my article on the 3 steps to calculating a pitcher’s ERA.

Some Pitchers Have an Infinity ERA

One of the rare anomalies that can occur with calculating ERA is that it’s possible for pitchers to have an ERA of infinity. Even the most enthusiastic fans are unaware of an ERA of infinity, but it makes sense once we break down that calculation.

Imagine a scenario where a pitcher comes into the game and they are not having their best day on the mound. They face 3 batters, give up an earned run, and fail to get any batters out. In this scenario, a pitcher’s ERA for the day would be infinity because they technically pitched 0 innings and it would be impossible to divide by 0.

While it’s possible for a pitcher’s ERA to be infinity for one particular day, there are a handful of pitchers who have a career ERA of infinity. To learn more, read how to get an infinity ERA, which also covers the 60+ pitchers who have a career ERA of infinity.

ERA Is Usually Calculated By Looking at Stats for the Season

While there is a formula for how to calculate ERA, the one thing missing from that formula is what time frame you need to look at in order to find the total number of earned runs and the total number of innings pitched needed to calculate ERA. Does ERA look at stats for the whole season?

As a general rule, ERA is calculated based on a pitcher’s season or a pitcher’s career, depending on the context. The ERA that displays during a baseball game is calculated based on that pitcher’s entire season while the stats you find online may look at both season stats and career stats.

While it’s possible for ERA to be calculated based on a single game, ERA is traditionally calculated based on a pitcher’s current season or their entire career. It really depends on what data you’re trying to find. But if you’re watching TV or you’re at a ballpark and see the ERA listed for a pitcher, it’s always based on the data from that pitcher’s current season.

A Good ERA for a Pitcher is Between 3.00 – 4.00

Shoulders-down view of a pitcher in a red jersey lifting his leg to deliver a pitch

Once we’ve calculated a pitcher’s ERA, the next step is to understand what that number means. We know that a lower ERA means a pitcher gives up fewer earned runs, but what exactly is a good ERA for a pitcher?

In the MLB, a good ERA for a pitcher is between 3.00 – 4.00. Most pitchers fall somewhere just above 4.00, so anything below a 4.00 is considered good.

However, there are plenty of pitchers that get below a 3.00 ERA. In fact, most starting pitchers who win the Cy Young award have an ERA that falls somewhere between 1.50 and 3.00, which is an outstanding ERA.

Read more about what is a good ERA in baseball.

Relief Pitchers Tend to Have Lower ERAs Than Starting Pitchers

One common misconception is that starting pitchers are better than relief pitchers. Often times you’ll hear coaches or players talk about how they want to make the opposing team use their bullpen as early as possible, which is due to the belief that it’s easier to hit off of a team’s relief pitcher.

However, relief pitchers tend to have a lower ERA than starting pitchers. While ERA by itself doesn’t necessarily mean a pitcher is good or bad, it does indicate that some teams struggle to hit off of relief pitchers.

If you look at the data I published in my article on what is a good ERA in baseball, you’ll see that relief pitchers have an average ERA of 3.97 while starting pitchers have an average ERA of 4.22 during the same time period. While the difference in ERA is not huge, it does show that relief pitchers tend to do a little better than starting pitchers when it comes to allowing earned runs.

However, closing pitchers seem to win the argument when it comes to which type of pitcher has the lowest ERA. Closing pitchers are a special type of relief pitcher and they mainly come into the game in high-pressure situations to finish a game.

Because closing pitchers throw fewer innings than other pitchers and because they only need to get 3 outs whenever they do enter the game, closing pitchers tend to have lower ERAs.

For more in-depth analysis on how ERAs compare between starting pitchers, relief pitchers, and closers, read more about what is a good ERA for a starting pitcher, what is a good ERA for a relief pitcher, and what is a good ERA for a closer.

ERA is Both a Good and Bad Stat

While there are benefits to looking at a pitcher’s ERA, like understanding how many earned runs a pitcher tends to give up, there are plenty of people who believe ERA is not a useful statistic and they would prefer to use other ways to measure the effectiveness of pitchers.

Some additional ways to measure a pitcher include Runs Allowed Per Nine Innings Pitched (RA9) and Fielding Independent Pitching (FIP), which are both considered an “advanced statistic” for pitching and go into more detail than ERA.

Another criticism people have about ERA is that it doesn’t always account for a pitcher’s ability. Instead, there are plenty of times where the defense was responsible for a run, but that run still counted as an earned run.

Different defensive players have different abilities and it’s not fair to judge a pitcher with a phenomenal defense to a pitcher with a terrible defense. The pitcher with the terrible defense is at a big disadvantage when it comes to ERA.

On the other hand, people who like using ERA say that ERA does filter out mistakes made by the defense so ERA is a good representation of the runs a pitcher is solely responsible for giving up. After all, when the defense makes an error, it is counted as an unearned run, which does not reflect in the pitcher’s ERA.

As you can see, there are a lot of pros and cons to using ERA as a statistic. Read more about the 4 pros and 4 cons of using ERA as a statistic to judge for yourself if you are the type of person who likes using ERA or is against using ERA.

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Steve Nelson

I'm the owner of Baseball Training World. I live in Denver, Colorado and I enjoy playing baseball in an adult baseball team in the surrounding area. Read more about Steve Nelson.