Baseball stats
What ERA means in baseball and how to calculate it
ERA means earned run average: the number of earned runs a pitcher allows per nine innings. Calculate it as 9 × earned runs ÷ innings pitched. Three earned runs in six innings produce a 4.50 ERA. A lower ERA is better because it means the pitcher allows fewer earned runs.
Sources and resources
- MLB ERA glossary — MLB's definition, formula, uses, and limits for earned run average.
- MLB earned-run glossary — MLB's explanation of which runs count against a pitcher's ERA.
- MLB unearned-run glossary — MLB's guide to runs caused by errors or passed balls that do not count in ERA.
- MLB innings-pitched glossary — MLB's guide to recording each out as one-third of an inning pitched.
What does ERA stand for in baseball?
ERA stands for earned run average. It estimates how many earned runs a pitcher allows for every nine innings pitched.
ERA uses a nine-inning scale even when a pitcher works fewer than nine innings in a game. It lets fans compare starters and relievers across different workloads.
How do you calculate ERA?
The formula is ERA = 9 × earned runs ÷ innings pitched. Multiply the pitcher's earned runs by nine, then divide by the innings pitched.
If a pitcher allows three earned runs in six innings, the calculation is 9 × 3 ÷ 6, which equals a 4.50 ERA. One earned run in seven innings produces a 1.29 ERA when rounded to two decimals.
- 3 ER in 6 IP: 9 × 3 ÷ 6 = 4.50 ERA
- 1 ER in 7 IP: 9 × 1 ÷ 7 = 1.29 ERA
- 0 ER in any number of recorded innings = 0.00 ERA
What is an earned run?
An earned run scores without the aid of an error or a passed ball. The official scorer reconstructs an inning without those defensive mistakes to decide which runs count against the pitcher.
Hits, walks, hit batters, wild pitches, balks, stolen bases, and many ordinary outs can all contribute to an earned run. A wild pitch is charged to the pitcher, so it does not make a run unearned by itself.
Do unearned runs count against ERA?
No. A run that scores because of an error or passed ball can be ruled unearned and left out of ERA. It still counts on the scoreboard and can affect the game's result.
The earned or unearned ruling belongs to the official scorer. Not every defensive mistake becomes an error, and the scorer must judge whether the run would have scored without the recorded error or passed ball.
How do partial innings work in an ERA calculation?
Each out is one-third of an inning pitched. A line of 6.1 IP means six innings plus one out, or 6⅓ innings. A line of 6.2 IP means six innings plus two outs, or 6⅔ innings.
Do not treat 6.1 IP as the decimal number 6.1 when calculating ERA. Convert the out notation to thirds first.
- 6.0 IP — six complete innings
- 6.1 IP — six innings and one out, equal to 6⅓
- 6.2 IP — six innings and two outs, equal to 6⅔
Is a higher or lower ERA better?
A lower ERA is better because it means the pitcher allows fewer earned runs per nine innings. A 2.50 ERA is better than a 4.50 ERA when the other context is similar.
League scoring, ballpark, defense, role, season, and workload all affect ERA. Compare pitchers from the same setting and use innings pitched to see how much work sits behind the rate.
Why can ERA be misleading for relievers?
A reliever often works only part of an inning, so one run can move the rate sharply. A reliever can also leave runners on base whose later earned runs remain charged to that pitcher.
ERA remains useful, but innings pitched, inherited runners, strikeouts, walks, home runs, role, and defense can explain parts of a pitcher's performance that ERA alone misses.
Track the pitchers and ERA lines you saw in person
A completed box score keeps each pitcher's innings, earned runs, strikeouts, walks, hits, and decision. Those lines can become part of your own record of pitchers witnessed live.
Log a completed game in Gamebook and it connects the official players and box score to your ballpark visit, seat, score, home runs, companions, photos, and memory.
Common questions
What does ERA stand for in baseball?
ERA stands for earned run average. It is the number of earned runs a pitcher allows per nine innings.
What is the formula for ERA?
ERA equals nine times earned runs divided by innings pitched: ERA = 9 × ER ÷ IP.
How do you calculate a 4.50 ERA?
Three earned runs in six innings produce a 4.50 ERA: 9 × 3 ÷ 6 = 4.50.
Is a higher or lower ERA better?
A lower ERA is better because it means the pitcher allows fewer earned runs per nine innings.
Do unearned runs count against ERA?
No. Runs ruled unearned because of an error or passed ball do not count in ERA, though they still count in the game's score.
Does an inherited runner count against a pitcher's ERA?
If a pitcher leaves a responsible runner on base and that runner later scores an earned run, the run remains charged to the pitcher who allowed the runner.
What does 6.1 innings pitched mean?
It means six complete innings plus one out, or 6⅓ innings. The .1 is baseball out notation, not one-tenth of an inning.
Can a pitcher have a 0.00 ERA?
Yes. A pitcher who has recorded at least one out and allowed no earned runs has a 0.00 ERA.
Why can ERA change quickly for a reliever?
Relievers work fewer innings, so one earned run can have a large effect on their per-nine-inning rate.
Can Gamebook track pitchers I have seen?
Yes. Log a completed game and Gamebook connects its official pitchers and box score to your ballpark visit, score, seat, photos, companions, and memory.