Earned Run Average (ERA) is one of baseball’s numerous statistics that helps evaluate the effectiveness of pitchers. Along with Wins (W) and Strikeouts (SO), ERA is the most widely used statistic for pitchers. However, how is ERA calculated?
ERA is calculated by dividing the total number of Earned Runs (ER) by the total number of Innings Pitched (IP), multiplying that number by 9, then rounding that number to two decimal places. A typical ERA for an MLB player is usually around 4.00, with the best players having scores closer to 2.00.
A low ERA is coveted by pitchers everywhere, and knowing how it works can help pitchers, managers, and coaches understand who is an effective pitcher. In this article, we’ll cover the 3 steps toward calculating a pitcher’s ERA and dive into why this number is useful.
Learn more about what is an ERA by reading A Beginner’s Guide to Baseball’s ERA Statistic.
3 Steps to Calculate ERA in Baseball
There may be over 100 statistics used in baseball, but ERA is one of the most widely used statistics for measuring the effectiveness of pitchers. And luckily, calculating a pitcher’s ERA is a simple 3 step process.
Step 1: Divide Earned Runs (ER) by Innings Pitched (IP)
The first step to calculating a pitcher’s ERA is to divide that pitcher’s Earned Runs by the number of Innings Pitched.
Remember, each out a pitcher gets counts as one-third of an inning pitched. So if a pitcher throws 5 innings, comes back into the game for the 6th inning, but only gets one out – they’ve pitched a total of 5 1/3 innings, or 5.33 innings.
Also, keep in mind that we are only using Earned Runs to calculate a pitcher’s ERA. If a runner scores because of an error on the defense, that run does not count towards a pitcher’s ERA. For more information on earned runs, read my other article on what makes a run an earned run.
On the rare occasion, pitchers will give up a run and fail to get one out. This means pitchers have technically thrown 0 innings and you’d have to divide by 0, which is not possible. This leads to the statistical anomaly of an infinite ERA. To learn more about this anomaly, read my other article on how to get an infinity ERA.
Step 2: Multiply By 9 (or the Standard Number of Innings in a Game)
After you’ve divided earned runs by the number of innings pitched, the next step is to calculate the result of that number by 9.
Here, we use the number 9 because there are 9 innings in a standard game of baseball. This will tell us how many runs, on average, a pitcher will give up in a 9-inning time frame.
However, there are some baseball leagues where the standard game does not last 9 innings. The best example of this would be a high school baseball game or a softball game, which generally lasts 7 innings. In these scenarios, you would find the ERA by multiplying by 7 instead of 9 because there are only 7 innings in a standard game.
The same logic is true if you are looking at youth leagues, like Little League. Some youth baseball leagues only last 6 innings, so we would multiply by 6 instead of 9 to find a pitcher’s ERA.
How Do You Calculate ERA for a 7 Inning Game?
The formula for calculating ERA for a 7-inning game would be to divide the number of Earned Runs (ER) by the number of Innings Pitched (IP), then multiply that number by 7. The result will be the ERA for a 7-inning game.
Step 3: Round to 2 Decimal Places
More often than not, you’ll end up with a number that contains a lot of decimal places. So the final step to finding a pitcher’s ERA is to take the number you got from Step 2 and round that to two decimal places.
Rounding to two decimal places makes it easier for everyone to read a pitcher’s ERA. And after all, it’s not very beneficial for players or coaches to know the ERA to that many decimal places.
ERA is Generally Calculated for the Entire Season
One question you may be wondering about is the time frame used when calculating a pitcher’s ERA. Do people usually calculate a pitcher’s ERA on a per-game basis, a weekly basis, or maybe a yearly basis?
As a general rule, the time frame for ERA is based on a pitcher’s season. While it’s possible to calculate ERA on a per-game or a weekly basis, players and coaches get more benefit from knowing a pitcher’s overall ERA for the season.
Why Calculating ERA is Beneficial
After we have the final ERA number, the next thing you may be wondering about is how this number is beneficial to anyone. But it turns out there are a few ways coaches and players find this number useful.
The biggest benefit of ERA is that it tells coaches and players a lot of information at once. Normally, ERA indicates how well a pitcher performs.
ERA is calculated only using Earned Runs, which means that any unearned runs do not count towards a pitcher’s ERA. So ERA tells a story of how effective or ineffective pitchers are on their own merit. The lower the ERA, the more effective a pitcher is at getting outs. For more info, read about why a low ERA is better than a high ERA.
Another big benefit is that ERA is easy to calculate and easy to understand. The only numbers someone needs to know are a pitcher’s earned runs and the number of innings they pitched. Once they have those 2 numbers, they can easily make the calculation.
The whole point of ERA is to calculate how many runs a pitcher is responsible for during a game. A pitcher who gives up more runs is usually considered worse than a pitcher who allows only a few runs to occur.
However, not everyone agrees that ERA is an effective tool for measuring a pitcher’s success. To better understand why ERA can be good or bad, read my other article on the 4 pros and 4 cons of using ERA as a statistic. After learning about these pros and cons, you’ll be able to judge for yourself if ERA is something worth evaluating.
Typical ERA for MLB
The MLB has been keeping track of the ERA of pitchers since 1880. While the method of calculating ERA hasn’t changed drastically over the decades, it has definitely gone up since the earliest days of baseball. Here is a quick summary of ERA by decade:
You can see the battle between pitchers and batters over the years. The 1900s and 1910s saw the rise of the spitball, which helps explain why the ERA is so low during those years. The 1990s and 2000s saw the Steroid Era through and shows in the average ERA dramatically increasing from previous decades.
The lowest league-wide ERA was in 1874 with an average of 2.19 and the highest was an astonishing 5.33 just 20 years later in 1894.
As you can see, it is a brutally tough battle between pitchers and batters. And although this table shows the average ERA for each decade, it doesn’t take into consideration what a “good” ERA is for pitchers.
In general, a “good” ERA for pitchers is somewhere between 3.00 and 4.00. To learn more about why a good ERA is between 3.00 and 4.00, read my other article on what is a good ERA in baseball, which also breaks down a good ERA for starting pitchers and relief pitchers.