Explainers
ERA Explained: How Earned Run Average Works
A practical explanation of ERA in baseball, how earned runs are calculated, and why innings pitched qualification matters on leaderboards.
The formula in plain language
Earned run average estimates how many earned runs a pitcher allows per nine innings. Multiply earned runs by nine, then divide by innings pitched. Lower is better.
Unearned runs—those that score because of errors or passed balls under scoring rules—are excluded from the earned-run bucket, which is why two pitchers with similar run totals can post different ERAs.
Qualification thresholds
Leaderboards require enough innings so that tiny samples do not dominate. Ballrecord applies standard playing-time qualification before ranking ERA leaders, which keeps one-start outliers from crowding out true rotation workhorses.
When evaluating a midseason race, check both the ERA itself and the innings total beside it. A sparkling mark in 40 innings is a storyline; the same mark in 120 innings is a Cy Young argument.
ERA’s modern companions
Defense, sequencing, and park effects all influence ERA. FIP, xFIP, and Statcast expected metrics help separate skill from noise. Use ERA as the traditional headline number, then verify with peripherals on the pitcher and team season pages.
Frequently asked questions
- What is a good ERA in MLB?
- It varies by season, but well below league average is strong. Always compare a pitcher to the same year’s league ERA rather than a fixed historical number.
- Why can ERA and FIP disagree?
- ERA includes outcomes influenced by balls in play and defense, while FIP focuses more on strikeouts, walks, hit batters, and home runs.
Continue in the record
Related notebook entries
- FIP vs ERA: Which Pitching Stat Should You Trust?Compare FIP and ERA in baseball, learn what each captures, and see when to trust peripherals over traditional earned run average.
- WHIP Explained: Walks Plus Hits Per Inning PitchedUnderstand WHIP in baseball, how it measures baserunner traffic, and how to pair it with ERA when evaluating pitchers.
- Quality Start vs Complete Game: Pitching Milestones ComparedCompare quality starts and complete games in MLB, why complete games became rare, and how to evaluate starters in bullpen eras.
- Innings Pitched Notation: Why .1 and .2 Mean OutsLearn how baseball innings pitched notation works, why .1 and .2 represent outs, and how Ballrecord displays pitcher workloads.