What is an ERA in Baseball? (Earned Runs Average)

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Baseball, a game woven into the fabric of American culture, is rich with statistics that tell the stories of legends past and present. Among these, the Earned Run Average (ERA) stands as a towering figure, casting light on the prowess of pitchers in the heat of competition. Whether you’re a casual fan or a seasoned analyst, understanding ERA unlocks a deeper appreciation of the game’s intricacies and the silent battles waged on the diamond.

What is an ERA in Baseball?

In baseball, the Earned Runs Average (ERA) is a statistic that measures a pitcher’s performance by calculating the average number of earned runs they allow per nine innings pitched. It’s a key indicator of a pitcher’s effectiveness, isolating their individual performance by excluding errors and focusing solely on the runs scored against them that result from opponents’ batting. The formula to calculate ERA is \(ERA = (Earned Runs \times 9) / Innings Pitched\). A lower ERA indicates a more effective pitcher, as it signifies that fewer earned runs have been scored against them, highlighting their skill at preventing the opposing team from scoring.

How to Calculate ERA

ERA, or Earned Run Average, is a statistic used in baseball to evaluate a pitcher’s effectiveness in preventing runs. It’s calculated by dividing the total number of earned runs allowed by the pitcher by the total number of innings pitched, and then multiplying the result by 9.

Here’s the ERA calculation formula:

ERA = ( Earned Runs / Innings Pitched ) * 9

To calculate ERA, follow these steps:

  1. Count Earned Runs Allowed: This includes any runs that scored due to the pitcher’s actions (e.g., hits, walks, hit batsmen) excluding errors made by the defense.
  2. Count Total Innings Pitched: This includes both complete innings and any fraction of an inning pitched. For example, if a pitcher completes 5 full innings and then pitches one out in the 6th inning before being replaced, it would be recorded as 5.1 innings pitched.
  3. Apply the Formula: Divide the earned runs allowed by the innings pitched, and then multiply the result by 9 to normalize it to a nine-inning game.

ERA Calculation with Example

Consider a scenario where a pitcher has pitched a total of 20 innings over several games and has allowed 5 earned runs during those innings. To calculate the ERA based on these statistics, follow the calculation steps outlined.

  1. Earned Runs Allowed: The pitcher has allowed 5 earned runs.
  2. Total Innings Pitched: The pitcher has pitched a total of 20 innings.
  3. Apply the Formula: Using the ERA formula, the calculation would be \(ERA = (5 / 20) * 9\).

Thus, the pitcher’s ERA is \(0.25 * 9 = 2.25\). This means that, on average, the pitcher allows 2.25 earned runs per 9 innings pitched, which is typically considered an excellent ERA in professional baseball.

What is a Good ERA in Baseball?

In baseball, the Earned Run Average (ERA) is a critical measure of a pitcher’s effectiveness, deeply influencing a team’s defensive strategy and game outcomes. An ERA between 3.00 and 4.00 is generally regarded as good, reflecting a pitcher’s ability to limit the opposition’s scoring and keep the game within reach for their team. Achieving an ERA below this range is considered excellent, as it demonstrates a pitcher’s dominance over hitters and their consistent performance in preventing runs. For instance, Clayton Kershaw, one of the most celebrated pitchers in recent history, boasts an ERA of 2.49 over his illustrious career. This figure not only highlights his exceptional skill and precision in pitching but also underscores his significance in the realm of professional baseball. A low ERA, like Kershaw’s, signifies a pitcher’s elite capability to thwart scoring attempts, cementing their status among the sport’s elite.

MLB ERA Leaders

All Time ERA Leaders

These all-time ERA leaders in MLB showcase some of the most dominant pitching performances in the history of the game:

Ed Walsh (1.82 ERA):

Teams: Chicago White Sox (AL), Boston Braves (NL)

Years: 1904–1917

Walsh’s remarkable career spanned over a decade, during which he consistently baffled hitters with his exceptional pitching. His career ERA of 1.82 remains unmatched and is a testament to his incredible skill on the mound.

Addie Joss (1.89 ERA):

Team: Cleveland Naps (AL)

Years: 1902–1910

Joss’s career with the Cleveland Naps was tragically cut short by his untimely death at the age of 31. Despite his brief career, Joss left an indelible mark on the game, boasting an impressive ERA of 1.89, which ranks among the best in history.

Jim Devlin (1.89 ERA):

Teams: Chicago White Stockings (NA), Louisville Grays (NL)

Years: 1875–1877

Devlin’s career predated the modern era of baseball, but his impact on the game is undeniable. With an ERA of 1.89, Devlin showcased unparalleled pitching prowess during his time in the National Association and National League.

Jack Pfiester (2.02 ERA):

Teams: Pittsburgh Pirates (NL), Chicago Cubs (NL)

Years: 1903–1904, 1906–1911

Pfiester enjoyed a successful career as a pitcher, particularly with the Chicago Cubs, where he was known for his consistency and effectiveness on the mound. His career ERA of 2.02 solidifies his place among the all-time greats.

Smoky Joe Wood (2.03 ERA):

Teams: Boston Red Sox (AL), Cleveland Indians (AL)

Years: 1908–1915, 1917–1922

Wood was a dominant force during the “Deadball Era,” known for his blazing fastball and devastating curveball. Despite facing formidable hitters of his time, Wood maintained an impressive ERA of 2.03 throughout his career, earning him a place among the top ERA leaders in MLB history.

Lowest Career ERA in MLB History

Ed Walsh (1.82 ERA):

Team: Chicago White Sox (AL)

Years: 1904–1917

The lowest career ERA in MLB history belongs to Ed Walsh, who spent his entire career with the Chicago White Sox.

With a record-setting career ERA of 1.82, the lowest in MLB history, Walsh’s performances were both awe-inspiring and record-breaking. His extraordinary 1908 season, boasting 40 wins, 269 strikeouts, and an ERA of 1.42, led the American League in wins and strikeouts, showcasing his dominance over hitters. Additionally, his no-hitter against the Boston Red Sox in 1911 further cements his legacy as one of the greatest pitchers in the history of baseball. His capacity to maintain an exceptional level of play, evidenced by his career totals of 195 wins and 1736 strikeouts, underlines Walsh’s incredible skill and resilience on the mound.

ERA Leaders in MLB (Modern era)

Transitioning into the modern era of baseball, the approach to pitching and game strategy has evolved, yet the objective of maintaining a low Earned Run Average (ERA) remains paramount for pitchers. Among the illustrious names that resonate in this era, Mariano Rivera stands out with an exceptional ERA of 2.21. Playing for the New York Yankees from 1995 through 2013, Rivera revolutionized the closer role, becoming a pivotal figure in the team’s success.

Not far behind, Clayton Kershaw of the Los Angeles Dodgers (NL) continues to etch his name into the annals of baseball history. Since his debut in 2008, Kershaw has maintained an impressive ERA of 2.49, showcasing consistency and extraordinary skill that has earned him numerous accolades, including multiple Cy Young Awards.

Also demanding recognition is Jacob deGrom, who began his career with the New York Mets (NL) and, as of 2023, plays for the Texas Rangers. DeGrom, known for his precision and powerful pitching, has managed to maintain an ERA of 2.53 since his debut in 2014. His achievements, including back-to-back Cy Young Awards, underscore his status as one of the premier pitchers in the game today.


The evolution of pitching in baseball, marked by the exceptional achievements of players like Ed Walsh, Mariano Rivera, Clayton Kershaw, and Jacob deGrom, showcases the sport’s dynamic nature and the inherent challenges of maintaining excellence over time. Their prowess on the mound, characterized by low ERAs and significant contributions to their teams, cements their legacies as some of the greatest pitchers in the history of the game. As baseball continues to evolve, the achievements of these athletes will remain a benchmark, inspiring future generations to excel and perhaps, redefine the standards of pitching excellence in the years to come.

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James Arnold
I'm James, and I live in Stanislaus County, California. I'm playing Baseball for many years, and I love this sport so much that I also encourage my kids (Danny and Sara) to play Baseball & Softball.