The standard baseball pitching statistic — earned runs allowed, scaled to a standard 9-inning game.
How it works
Dividing earned runs by innings pitched and multiplying by 9 gives ERA, the earned runs a pitcher would be expected to allow over a full 9-inning game at the same rate.
What this does not include
This does not include unearned runs (runs that scored due to fielding errors), which are excluded from ERA by definition.
How to use this calculator
- Enter earned runs allowed and innings pitched.
A worked example
5 earned runs allowed over 9 innings pitched → (5 ÷ 9) × 9 = ERA 5.00.
2 earned runs over 6 innings → (2 ÷ 6) × 9 = ERA 3.00.
What the variables mean
| Variable | Meaning |
|---|---|
| Earned runs | Runs charged to the pitcher, excluding those caused by fielding errors |
| Innings pitched | Total innings the pitcher worked |
Edge cases worth knowing
ERA is scaled to a 9-inning game, which is why the formula multiplies by 9 rather than just dividing runs by innings — it puts pitchers who worked different numbers of innings on a comparable scale.
Zero innings pitched makes ERA undefined — there’s no game length to scale against, so the calculator returns no result.
Frequently asked questions
Why is ERA scaled to 9 innings?
A standard baseball game is 9 innings, so scaling to that length lets pitchers with different amounts of playing time be compared on the same basis.
What counts as an “earned” run?
A run that scored without the help of a fielding error or passed ball — runs that resulted from defensive mistakes are excluded from a pitcher’s ERA.
What’s considered a good ERA?
Generally, an ERA under 3.00 is considered excellent at the professional level, though what’s “good” varies by league, era, and level of play.
