# What is my ERA?

Computes a pitcher’s earned run average (ERA), the earned runs allowed per nine innings, from earned runs and innings pitched in box-score notation (6.2 is 6⅔ innings).

- Page: https://www.acalculator.org/sports/era-calculator
- JSON spec: https://www.acalculator.org/sports/era-calculator.json
- Version: 3bcf95dc6291

## Default answer

Example with the default inputs (Earned runs 25, Innings pitched 90.1, Innings in a game 9): The ERA is 2.49 (earned runs 25, innings pitched 90⅓).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| er | Earned runs | The earned runs charged to the pitcher. |
| ip | Innings pitched | The innings pitched in box-score notation: .1 is one out and .2 is two outs, so 6.2 means 6⅔ innings. |
| inn | Innings in a game | The innings in a regulation game that the ERA is scaled to: 9 in MLB and college baseball. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| era | ERA | Earned runs allowed per game of the chosen length: earned runs × innings in a game ÷ innings pitched, written with exactly two decimals as box scores print it (2.00). |
| innings | Innings pitched | The innings pitched with the partial inning as a fraction, for example 6⅔. |
| outs | Outs recorded | The innings pitched counted in outs: 3 per whole inning plus the partial outs. |
| perInning | Earned runs per inning | Earned runs ÷ innings pitched. |

## Method

ERA = earned runs × innings in a game ÷ innings pitched, with innings pitched in thirds (outs ÷ 3), so 6.2 is 20 outs, 6⅔ innings.

## Assumptions

- Innings pitched use box-score notation: the digit after the point counts outs (.1 is one out, .2 is two outs). Any other decimal has no answer.
- The ERA is scaled to 9 innings unless you change Innings in a game (a league of 7-inning games may use 7).
- Earned runs are whole numbers from 0 to 100,000; innings pitched are up to 100,000.
- With earned runs but no outs recorded the ERA is infinite, and with no outs and no runs there is none; both give no answer.
- The ERA is shown to two decimal places, rounded half up from the exact fraction.

## Worked examples

1. er = 3, ip = 4, inn = 9 gives era = 6.75, innings = 4, outs = 12, perInning = 0.75. Source: Baseball-Reference, Earned Run Average glossary (3 ÷ 4 × 9 = 6.75). https://www.baseball-reference.com/glossary/earned-run-average/.
2. er = 2,147, ip = 7,356, inn = 9 gives era = 2.63, outs = 22,068. Source: Baseball-Reference, Earned Run Average glossary (2,147 ÷ 7,356 × 9, shown as 2.63). https://www.baseball-reference.com/glossary/earned-run-average/.
3. er = 3, ip = 9.1, inn = 9 gives era = 2.89, innings = 9⅓, outs = 28. Source: 3 × 9 × 3 ÷ 28 = 81/28 = 2.89 (formula from Baseball-Reference, https://www.baseball-reference.com/glossary/earned-run-average/).
4. er = 58, ip = 180.2, inn = 9 gives era = 2.89, innings = 180⅔, outs = 542. Source: 58 × 9 × 3 ÷ 542 = 783/271 = 2.89 (formula from Baseball-Reference, https://www.baseball-reference.com/glossary/earned-run-average/).
5. er = 10, ip = 35, inn = 7 gives era = 2.00, perInning = 0.285714.
6. er = 0, ip = 0.2, inn = 9 gives era = 0.00, innings = ⅔, outs = 2.

## FAQ

### How do I calculate ERA?

Multiply the earned runs by 9 and divide by the innings pitched. A pitcher who allows 3 earned runs in 4 innings has an ERA of 3 × 9 ÷ 4 = 6.75.

### What do innings like 6.1 and 6.2 mean?

Box scores count a partial inning in outs: 6.1 means 6 innings and 1 out (6⅓ innings) and 6.2 means 6 innings and 2 outs (6⅔). The calculator reads them that way, so 6.2 is never treated as 6.2 innings. A third out makes a whole inning, so 6.3 is not used.

### What is a good ERA?

Lower is better, because ERA counts the runs a pitcher allows. Compare an ERA with the league average for the same league and season, which stat sites such as Baseball-Reference publish every year: a pitcher well below the average had a strong season.

### What is the difference between a run and an earned run?

An earned run is a run the pitcher is charged with because it scored without help from a fielding error or a passed ball. The official scorer decides which runs are earned. Only earned runs go into ERA.

### Can an ERA be infinite?

Yes. A pitcher who gives up an earned run before recording a single out has 0 innings pitched, so the ERA would divide by zero. Stat pages print it as ∞; the calculator says it is infinite and shows no number.

### How is ERA calculated for 7-inning games?

Set Innings in a game to 7. The formula becomes earned runs × 7 ÷ innings pitched, so 10 earned runs in 35 innings is an ERA of 2.00. Leagues differ, so check which length your league uses.

## Sources

- Baseball-Reference, Earned Run Average (ERA) glossary: ERA = (earned runs ÷ innings pitched) × 9; worked examples 3 ER in 4 IP = 6.75, 2,147 ER in 7,356 IP = 2.63. https://www.baseball-reference.com/glossary/earned-run-average/
- Wikipedia, Earned run average (ERA = 9 × earned runs ÷ innings pitched; infinite ERA with no outs). https://en.wikipedia.org/wiki/Earned_run_average