Baseball Glossary › Earned Run Average
Earned Run Average (ERA)
Earned run average (ERA) is the number of earned runs a pitcher allows per nine innings. Multiply earned runs by 9 and divide by innings pitched. Runs that score because of an error or a passed ball are unearned and left out, so ERA tries to measure only the runs that are the pitcher's fault.
Formula
Worked example from Official Baseball Rule 9.21(e): a pitcher allows 3 earned runs in 9 1/3 innings.
ERA = 3 x 9 / 9.333 = 27 / 9.333 = 2.89
Note: 9 1/3 innings is written 9.1 in a box score, but you must use 9.333 in the math.
Athletics example: Rollie Fingers
Rollie Fingers, a key arm on the 1972 to 1974 champions, finished his career with a 2.91 ERA over 1701.1 innings. See the full career line on the Rollie Fingers player page.
Earned runs allowed per nine innings: 2.91
Our database stores the finished ERA rather than raw earned-run totals, so this example shows the published figure rather than recomputing it. Career MLB totals from our player database (MLB Stats API).
What to Know
ERA counts only earned runs. Runs allowed counts every run charged to the pitcher, earned or not, which is why a pitcher's runs total can be higher than his ERA suggests. Runners a pitcher leaves on base still count against him if they later score.
ERA vs WHIP: ERA measures runs, while WHIP measures baserunners per inning. A pitcher can allow plenty of baserunners and still post a low ERA by stranding them, which often does not last. That is why analysts pair ERA with fielding independent pitching, which strips out defense and luck on balls in play.
What counts as good shifts with the league's run environment. FanGraphs' rule-of-thumb table, which it describes as an estimate, puts roughly 3.75 at average, 3.00 as great and 2.50 as excellent. Relievers usually post lower ERAs than starters because they pitch short, high-effort outings.
Frequently Asked Questions
What does ERA mean in baseball?
ERA stands for earned run average. It is the average number of earned runs a pitcher allows per nine innings, calculated as 9 times earned runs divided by innings pitched. Lower is better.
How do you calculate ERA?
Multiply earned runs allowed by 9, then divide by innings pitched. Convert partial innings first: 6.1 innings is 6 1/3, or 6.333, and 6.2 innings is 6 2/3, or 6.667.
What is a good ERA in baseball?
It depends on the season's scoring level, but FanGraphs' rough guide treats about 3.75 as average, 3.00 as great and 2.50 or lower as excellent. Compare a pitcher with his league rather than a fixed number.
What is the difference between an earned run and an unearned run?
An earned run scores without the help of an error or passed ball. An unearned run would not have scored without that defensive mistake, as judged by the official scorer. Only earned runs count in ERA.
Does a reliever's ERA include runners he inherits?
No. Runners left on base by the previous pitcher are charged to that previous pitcher if they score. A reliever is charged only for runners who reached base against him.
Why do relievers usually have lower ERAs than starters?
Relievers pitch short outings and can throw at full effort for every batter, and their ERA can depend on how the next reliever handles runners they leave behind. Starters must pace themselves over many innings.
Related Terms
Sources
- MLB.com Glossary: Earned Run Average (ERA)
- MLB.com Glossary: Earned Run (ER)
- FanGraphs Sabermetrics Library: ERA
- Official Baseball Rules 2026 (MLB)
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