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ERA (Earned Run Average)

General

Earned Run Average

A baseball pitching statistic measuring earned runs allowed per nine innings pitched, standardizing performance while excluding runs caused by fielding errors.

Definition

ERA, or Earned Run Average, is one of the most widely used statistics for evaluating a baseball pitcher's effectiveness. It measures the average number of earned runs a pitcher allows per nine innings pitched, standardizing performance to a full-game basis so pitchers who throw different numbers of innings can be fairly compared against one another.

The "earned" qualifier is central to the statistic: only runs that score through legitimate offensive play — hits, walks, sacrifice flies, and similar plays — count toward ERA, while runs that score because of a fielding error or passed ball are excluded as unearned. This distinction is meant to isolate the pitcher's own performance from mistakes made by their teammates on defense. The ERA Calculator takes earned runs allowed and innings pitched as inputs and returns the standardized nine-inning rate.

Because ERA is expressed on a per-nine-innings basis, it allows direct comparison between a starting pitcher who logs six or seven innings per outing and a relief pitcher who might only throw one or two innings at a time. A lower ERA indicates a pitcher is allowing fewer earned runs relative to the innings they pitch, making ERA a core metric for ranking pitchers, setting award consideration, and negotiating contracts, even though it does not account for factors like bullpen support or team defense quality beyond the earned/unearned distinction.

Formula

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

Where Earned Runs Allowed is the total number of runs scored against the pitcher that are not attributable to fielding errors or passed balls, and Innings Pitched is the total innings that pitcher has thrown, expressed as a decimal where each out counts as one-third of an inning.

Worked Example

A starting pitcher allows 3 earned runs over 6 innings pitched in a single outing, and this is their full-season total across all appearances as well.

ERA = (3 / 6) × 9 = 0.5 × 9 = 4.50

A season-long ERA of 4.50 would place this pitcher roughly around league average, indicating they allow about 4.5 earned runs for every 9 innings they pitch, which is a useful year-over-year benchmark for tracking whether their performance is improving or declining.

Key Things to Know

  • ERA excludes runs caused by defensive errors: only earned runs, meaning those that scored through legitimate offensive play, are counted, isolating the pitcher's own performance from teammates' fielding mistakes.
  • The nine-inning standardization enables fair comparisons: multiplying by 9 and dividing by innings pitched lets a reliever who throws limited innings be compared fairly against a starter who throws many more.
  • Partial innings are recorded as thirds, not tenths: a box score showing 5.2 innings pitched actually represents 5 and two-thirds innings in the underlying ERA calculation, not 5.2 innings as a decimal.
  • ERA is independent of win-loss record: because run support from a pitcher's own offense has no bearing on ERA, it is generally viewed as a purer measure of individual pitching skill than wins and losses.
  • Lower ERA values indicate stronger pitching performance: an ERA below 3.00 is typically considered excellent at the professional level, while values above 5.00 signal below-average performance for a starting pitcher.

Related Calculators

ERA Calculator →Calculate a baseball pitcher's earned run average (ERA) from earned runs and innings pitched in seconds. Free tool for players, coaches, and fantasy baseball fans.

Frequently Asked Questions

An earned run is any run that scores without the help of a fielding error or a passed ball, meaning the batting team advanced runners and scored through legitimate offensive play. Runs that only scored because of a defensive misplay are classified as unearned and are excluded from ERA.
In Major League Baseball, an ERA below 3.00 is generally considered excellent, an ERA between 3.00 and 4.00 is solid, and an ERA above 5.00 is considered poor for a starting pitcher. League average ERA typically hovers around 4.00 depending on the era and offensive environment.
ERA is standardized to nine innings because a full professional baseball game consists of nine innings, so multiplying by 9 and dividing by innings pitched allows fair comparison between pitchers who throw different numbers of innings. Without this adjustment, a reliever who pitches only a few innings per outing could not be meaningfully compared to a starter who regularly pitches six or seven innings.
Partial innings are recorded in thirds, where one out equals 0.1 innings pitched, two outs equal 0.2 innings pitched, and a full inning equals 1.0 in official scoring notation, though the underlying math treats these as one-third and two-thirds of an inning. For example, 5 and two-thirds innings pitched is recorded as 5.2 in box scores but used as 5.667 in the actual ERA formula.
No, ERA is completely independent of win-loss record, since wins and losses depend heavily on how much run support a pitcher's own team provides. A pitcher can post an excellent ERA while accumulating losses if their team fails to score runs, which is why ERA is generally considered a better indicator of individual pitching performance than win totals.
ERA is calculated as earned runs divided by innings pitched, multiplied by 9, so here that is 4 divided by 8, times 9, which equals 4.50. This 4.50 ERA reflects that the pitcher would be expected to allow 4.5 earned runs per nine innings pitched at that same rate.