What does era mean in baseball

The ERA Plan: A New Approach to Evaluating Pitchers

Baseball has always loved stats. Batting averages, home runs, RBIs - the numbers help us understand and compare players. But when it comes to pitchers, wins and losses don’t tell the whole story. That’s why baseball developed a stat called ERA.

ERA stands for Earned Run Average. It measures the average number of earned runs a pitcher surrenders per 9 innings pitched. An earned run is any run that scores without the help of an error or passed ball - basically runs the pitcher is directly responsible for.

ERA provides a much better metric for evaluating pitchers than simple wins and losses. A pitcher can lose a game 1-0 but pitch fantastically. Or he can get shelled for 6 runs but his offense bails him out. ERA cuts through all that noise. It isolates the pitcher’s performance.

Lower ERAs are better. An ERA under 3 is excellent while ERAs over 5 are poor. The very best starters maintain ERAs under 2 over a full season. Relievers often have lower ERAs since they rarely face batters more than once.

In the modern game, ERA has become fundamental to assessing pitchers. Teams rely on it to measure a pitcher’s ability and make roster decisions. Fans use it to compare hurlers. The lower the ERA, the better the pitcher performed independent of other factors.

While no stat tells the whole story, ERA gives us an elegant and insightful metric. By focusing only on earned runs allowed, it strips away noise and helps us evaluate pitchers based on their actual performance. For over 100 years, it has brought clarity to the most important job on the field - getting outs.

Calculating a Pitcher’s ERA

What is ERA?

ERA (Earned Run Average) is one of the most commonly used statistics to measure a pitcher’s performance in baseball. It shows the average number of earned runs a pitcher allows per 9 innings pitched. Calculating ERA is simple once you understand the basic components.

What is an Earned Run?

An earned run is any run that scores without the benefit of a fielding error or passed ball. It reflects runs that scored purely on the pitcher’s performance. If a runner reaches base on an error and later scores, that run is unearned and does not count toward ERA.

The Formula

The formula for calculating ERA is:

ERA = (Earned Runs Allowed x 9) / Innings Pitched

The “9” represents the number of innings in a complete game. This scales the statistic to project the number of earned runs a pitcher would allow if they pitched a full game.


Here is an example to illustrate the ERA calculation:

ERA = (2 Earned Runs x 9) / 5 Innings Pitched = 18 / 5 = 3.60

So Pitcher A’s ERA over those 5 innings is 3.60. This means he allowed an average of 3.60 earned runs per 9 innings pitched.

Interpreting ERA

The lower a pitcher’s ERA, the better he performed. An ERA below 4.00 is generally considered excellent. Top pitchers often have ERAs in the 2.00-3.00 range during their peak seasons.

Calculating ERA helps assess a pitcher’s ability to prevent runs. It is one of the key metrics to evaluate performance and compare pitchers across MLB. This simple but insightful statistic has been used for over 100 years.

What are Earned Runs? Earned Runs vs. Unearned Runs

The Difference Between Earned Runs and Unearned Runs in Baseball


An earned run is any run that scores without the contribution of an error or passed ball. It reflects runs that scored exclusively through the opposing team’s batting and base running abilities. Earned runs are charged to the pitcher - they go on his record and are used to calculate his ERA.


For example, if a pitcher gives up a home run, that run counts as earned since the batter got a hit against the pitcher without any other factor involved. Or if the pitcher walks a batter, hits a batter, or gives up a string of hits that allows a run to score, those are earned runs since that batter reached base and scored due to the pitcher’s pitching skills.

What are Unearned Runs?


An unearned run is a run that scores with the help of an error, passed ball, or any kind of defensive mistake. Even if the pitcher gives up hits and walks to put runners on base, if they later score due to a fielding error, the runs are classified as unearned.

Relation to Pitcher’s Stats

Unearned runs are not charged to the pitcher’s ERA - they do not count against the pitcher’s pitching stats. For example, if a pitcher gets several batters out and has two outs in the inning but a fielder makes an error that allows a run to score, that run would be unearned. The logic is that with perfect defense, the pitcher would have been out of the inning without allowing a run.

Importance of the Distinction

Only earned runs factor into a pitcher’s ERA. Unearned runs are tracked separately. This allows ERAs to better reflect a pitcher’s actual performance and skill in preventing opposing batters from getting on base and scoring.

Gather the Data - Calculating ERA

How to Calculate a Pitcher’s ERA

Earned Runs Allowed

Add up the number of earned runs the pitcher allowed over the course of the season. Earned runs are runs that score without the benefit of a fielding error or passed ball. For example, let’s say a pitcher allowed 82 earned runs over the season.

Innings Pitched

Add up the total number of innings the pitcher pitched during the season. For our example, let’s say the pitcher pitched 210 innings.

Calculate Equivalent 9-Inning Games

Multiply the number of innings pitched by 9 to calculate the equivalent number of 9-inning games. In our example, 210 x 9 = 1,890.

Divide Earned Runs by Equivalent Innings

Divide the number of earned runs allowed by the number of equivalent 9-inning games. In our example:

82 earned runs / 1,890 equivalent innings = 0.043

Multiply by 9 for ERA

Multiply this result by 9 to calculate the ERA over 9 innings.

0.043 x 9 = 0.39 ERA

So for our example pitcher, their season ERA was 0.39 earned runs allowed per 9 innings pitched. This process can be followed for any pitcher over any season to calculate their ERA and evaluate their performance. Consistently low ERAs around 3 or less are considered very good.

What is ERA? - Good vs. Bad ERA

Evaluating Pitcher Performance: Good vs. Bad ERA

ERA, or earned run average, is a statistic that measures the number of earned runs a pitcher allows per 9 innings pitched on average. It shows how effective a pitcher is at preventing runs.

What is a Good ERA?

Below 4.00 is Good

An ERA below 4.00 is generally considered good for a starting pitcher in MLB. The league average ERA tends to be in the mid-3.00s, so anything under that benchmark means the pitcher is better than average at preventing runs.

Ideal ERAs are Sub-3.00

An ERA between 3.00 and 3.50 is very solid, and an ERA under 3.00 is excellent. The best pitchers in baseball will often post ERAs in the 2.00 range during their peak seasons.

Ideally, teams want their starters to have ERAs below 4.00. The lower the ERA, the better chance a pitcher gives their team to win.

What is a Bad ERA?

Above 5.00 is Poor

An ERA above 5.00 is usually considered poor for an MLB starting pitcher. Anything above 5.50 is very bad and means the pitcher is one of the least effective at preventing runs.

Over 6.00 Means Rotation Trouble

If a starter has an ERA over 6.00, they are likely close to losing their rotation spot. Relief pitchers can sometimes get away with higher ERAs given their small sample size of innings. But for starters who throw 170+ innings in a season, an ERA over 5.00 signifies they are giving up too many runs.

The Gray Area: 4.00 to 5.00 ERA

The range of 4.00 to 5.00 is a gray area for pitcher performance. An ERA here means the pitcher is below average and mediocre, but not completely terrible. Teams will often tolerate ERAs of 4.30-4.80 from their 4th and 5th starters. But it’s not a range pitchers want to be in long-term if they want to be considered high-quality starters.

In summary, sub-4.00 is good, above 5.00 is bad, and 4.00-5.00 is average for MLB starter ERAs. By evaluating a pitcher’s ERA, we can gauge their overall effectiveness and value to their team.

Comparison and key differences between starters and relievers

The Roles of Starters and Relievers in Baseball

Number of Innings Pitched

The most obvious difference between starters and relievers is the number of innings pitched per game. Starters typically pitch 5-7 innings or even complete games, while relievers may pitch just one inning. Starters pace themselves to maintain effectiveness over a longer outing, while relievers can exert maximum effort for a short stint.

Earned Run Averages

Due to fewer innings pitched, relievers tend to have lower ERAs than starters. In 2022, the average MLB starter had an ERA of 4.07, while the average reliever ERA was 3.52. The limited innings make it easier for relievers to limit runs. One bad inning won’t drastically inflate a reliever’s ERA like it can for a starter.

Leverage Situations

While starters face lineups multiple times through, relievers often enter in high-leverage situations like the late innings of close games. Teams try to use their best relievers when the game is on the line. Thus, relievers pitch in more pressurized scenarios that magnify good or bad performances.

Pitch Repertoires

Starters need a variety of pitches to maintain effectiveness facing batters multiple times. Relievers, however, can rely more on one or two “out” pitches and don’t need the same pitch diversity. Their short stints enable them to exert maximum effort on their best pitches.

Importance of Both Roles

While there are certainly exceptions, most MLB teams structure their pitching staffs around this typical starter/reliever dichotomy. The different roles lead to tactical decisions for managers on when to pull their starters and which relievers to use in key situations late in games. Both starters and relievers are integral for pitching success.

The Lowest Single-Season ERAs - Notable ERAs in History

Bob Gibson’s 1.12 ERA in 1968


In 1968, Bob Gibson posted an astonishing 1.12 ERA across 304.2 innings for the St. Louis Cardinals. This remains the lowest ERA ever recorded for a starting pitcher in a single season. Gibson allowed just 38 earned runs all year while striking out 268 batters and winning 22 games. His dominance helped lead the Cardinals to a World Series championship that season.

Dwight Gooden’s 1.53 ERA in 1985


Another remarkable feat was posted by Dwight Gooden of the New York Mets in 1985. In his age 20 season, Gooden recorded a 1.53 ERA over 276.2 innings pitched. He gave up just 35 earned runs all season with 268 strikeouts. Gooden’s performance helped him achieve the pitching Triple Crown, as he also led the majors in wins and strikeouts that year.

The Best Career ERAs

Earned run average (ERA) is a statistic used in baseball to measure a pitcher’s effectiveness. It’s one of the most important pitching stats as it represents the number of earned runs allowed by a pitcher on average per nine innings. Here are the top 5 Major League Baseball pitchers with the best career ERAs:

  1. Ed Walsh (1.82 ERA): Ed Walsh, who played in the early 1900s for the Chicago White Sox, holds the record for the best career ERA in MLB history.
  2. Addie Joss (1.89 ERA): Addie Joss, another early 1900s pitcher, played mostly for the Cleveland Naps (now Guardians).
  3. Jim Devlin (1.89 ERA): Jim Devlin pitched in the late 1800s and early 1900s, primarily for the Louisville Colonels.
  4. Jack Pfiester (2.02 ERA): Jack Pfiester played in the 1880s for the Philadelphia Athletics.
  5. Smoky Joe Wood (2.03 ERA): Smoky Joe Wood pitched in the early 1900s for the Boston Red Sox. It’s important to note that that baseball was a different game in the era when these pitchers played. The “dead ball” era, which lasted from roughly 1900 to 1920, saw lower scoring games and better pitching performances overall.

Mariano Rivera’s 2.21 ERA


When looking at careers, Mariano Rivera stands out with the lowest ERA in MLB history. The legendary New York Yankees closer maintained a 2.21 ERA over 1,283.2 innings from 1995 to 2013. His consistency and longevity in the unrelenting pressure of New York was astounding. Rivera held the career saves record when he retired.

Clayton Kershaw’s 2.48 Career ERA


Among starting pitchers, Clayton Kershaw has logged the best career ERA. His 2.48 ERA ranks first all-time among qualified starters. Since debuting in 2008, Kershaw has kept his ERA below 3.00 every year except for his rookie season. The Los Angeles Dodgers ace has won 3 Cy Young Awards and continues to build his Hall of Fame resume.

While the game has evolved over the decades, these historic ERAs remain almost unthinkable feats. The combination of dominance, consistency, and longevity demonstrated by pitchers like Gibson, Gooden, Rivera, and Kershaw may never be replicated. Their mastery on the mound allowed them to set records that stand the test of time.

The Limitations of Using ERA to Evaluate Pitchers

Defense Impacts ERA

ERA (earned run average) is a statistic that measures the number of earned runs allowed by a pitcher per nine innings pitched. It is one of the most commonly cited metrics for evaluating pitching performance. However, ERA has some important limitations that need to be considered when assessing pitchers.

Fielding Influences Scoring

One major limitation of ERA is that it is heavily influenced by the quality of the defense behind the pitcher. A pitcher with strong defenders committing few errors will tend to have a lower ERA than a pitcher with weak defense that makes more mistakes. The ability of the fielders to convert batted balls into outs impacts the number of runs scored against a pitcher, regardless of how well the pitcher actually performs.

For example, a groundball pitcher with sure-handed infielders will give up fewer runs than if that same pitcher had shaky defenders. The pitchers’ ERAs may differ significantly, even with similar pitching abilities. This makes it challenging to accurately judge pitchers who play for teams with varying defensive strengths based on ERA alone.

Ballpark Factors Affect ERA

Another limitation of ERA is that it does not account for the ballpark where the pitcher plays. Some ballparks favor pitchers more than others due to their dimensions, weather patterns, and other factors.

Pitcher Friendly Environments

A pitcher with a high ERA pitching in a hitter-friendly park might actually be more skilled than a pitcher with a lower ERA in a pitcher-friendly environment. Their ERAs may not reflect that accurately.

Run Support Impacts ERA

Additionally, ERA only measures runs allowed, which is heavily dependent on factors out of the pitcher’s control. The run support provided by a team’s offense affects ERA.

Win-Loss Record Influenced by Offense

A pitcher on a high-scoring team can win games despite giving up a lot of runs. Meanwhile, a pitcher with little run support will lose more games even with a low ERA. This makes it difficult to objectively judge pitchers based on ERA without context.

In summary, while ERA is a useful statistic, it has limitations due to the influence of defense, ballpark factors, run support, and other variables. Assessing pitchers solely on ERA does not necessarily capture their true talent and value. ERA needs to be considered as part of a holistic evaluation along with other metrics to accurately analyze pitching performance.


In baseball, one of the most important stats for pitchers is ERA, which stands for earned run average. ERA measures the average number of earned runs a pitcher gives up per 9 innings pitched. It provides insight into a pitcher’s effectiveness and skill in preventing runs. A lower ERA is better - it means the pitcher is giving up fewer runs.

ERA only considers earned runs, not runs scored due to errors or passed balls. This makes it a more accurate reflection of the pitcher’s performance. ERA accounts for external factors like ballpark effects and team defense. This standardized metric allows for comparison between pitchers across different teams and seasons.

Monitoring ERA is crucial in baseball. It can indicate when a pitcher is struggling or excelling. ERA leaders are highly valued in fantasy leagues and MLB award considerations like the Cy Young. An ERA under 3 is considered excellent while an ERA over 5 is poor. The all-time lowest single season ERA is 1.12 by Bob Gibson in 1968.

In summary, ERA is a vital statistic in evaluating pitchers. It provides a snapshot of their ability to minimize runs and succeed at their primary objective on the mound. ERA enables insightful comparisons to better understand pitching quality.

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