How this calculator works
You enter two things: the earned runs a pitcher has allowed and the innings they pitched. The calculator multiplies earned runs by nine, divides by innings, and returns the ERA per nine innings. Innings can be typed as a true decimal or in the baseball convention of innings-plus-outs — 6.2 for six innings and two outs — and the tool converts it correctly either way. ERA is usually shown to two decimal places; if you need to round a value by hand, the rounding calculator handles that, and the general calculators hub has the rest of the everyday tools.
The formula
ERA = (9 × Earned Runs) ÷ Innings Pitched
Innings Pitched = full innings + (outs ÷ 3)
Example: 3 earned runs in 6.0 innings is (9 × 3) ÷ 6 = 4.50. The multiplier is 9 because a regulation MLB game is nine innings; fastpitch softball uses 7 instead. Each out counts as one-third of an inning, so 6 innings and 2 outs is 6.667 innings, not 6.2.
Worked examples
Example 1 — a quality start
- Earned runs:
- 2
- Innings pitched:
- 7.0 innings
- Numerator: 9 × 2 = 18
- Divide by IP: 18 ÷ 7 = 2.571…
- Round to 2 dp: 2.57
ERA: 2.57
Two earned runs over seven innings is a strong outing — comfortably inside the 'solid' band for a modern starter.
Example 2 — a short relief appearance
- Earned runs:
- 1
- Innings pitched:
- 0.2 (2 outs) = 0.667 innings
- Convert outs: 2 outs ÷ 3 = 0.667 innings
- Numerator: 9 × 1 = 9
- Divide by IP: 9 ÷ 0.667 = 13.50
ERA: 13.50
Over tiny samples ERA swings wildly — one earned run in two-thirds of an inning produces a double-digit ERA. This is why ERA is only meaningful over a reasonable number of innings.
Reference data
| Recorded IP | Meaning | Decimal innings |
|---|---|---|
| 6.0 | 6 innings, 0 outs | 6.000 |
| 6.1 | 6 innings, 1 out | 6.333 |
| 6.2 | 6 innings, 2 outs | 6.667 |
| 7.0 | 7 innings, 0 outs | 7.000 |
Key facts
- ERA equals earned runs divided by innings pitched, multiplied by nine — the number of innings in a regulation MLB game.
- In innings-pitched notation, 6.1 means six innings and one out (6.333 innings) and 6.2 means six innings and two outs (6.667), because each out is one-third of an inning.
- An earned run is one charged to the pitcher without the help of a fielding error or passed ball.
- In modern MLB an ERA below 4.00 is considered solid and below 3.00 elite, though the benchmark moves with the league's run-scoring environment.
Who should use this and when
Coaches, players, fantasy managers and fans all use ERA to compare pitchers on a level footing. It is most reliable over a full season or a solid block of innings; over a single short outing it can be wildly misleading, as the relief example above shows. Use it alongside other measures — WHIP, FIP, strikeout and walk rates — rather than on its own, and remember it credits the pitcher only for earned runs, so a shaky defence can flatter an ERA while the raw runs allowed tell a different story.
Tips and common pitfalls
- Read the decimal correctly. 6.1 innings is six-and-one-third, not six-and-one-tenth — convert outs before dividing.
- Use earned runs, not total runs. Unearned runs from errors do not count toward ERA.
- Beware small samples. A handful of innings can produce an extreme ERA that says little about true skill.
- Match the multiplier to the game. Use 9 for baseball and 7 for fastpitch softball.
Frequently asked questions
What is ERA in baseball?+
ERA stands for Earned Run Average. It is the average number of earned runs a pitcher gives up per nine innings — the length of a regulation game — which makes starters and relievers comparable on the same scale regardless of how many innings each has thrown.
How do I calculate ERA?+
Use ERA = (9 × Earned Runs) ÷ Innings Pitched. For example, a pitcher who allows 3 earned runs in 6 innings has an ERA of (9 × 3) ÷ 6 = 4.50. The calculator does this for you and accepts innings entered either as decimal IP or as innings plus outs.
What is a good ERA?+
In modern MLB an ERA under 4.00 is considered solid and under 3.00 is elite. What counts as 'good' shifts with the era and the league's run-scoring environment, so a 4.00 in a high-scoring season is more impressive than the same number in a low-scoring one.
What is the difference between earned and unearned runs?+
Earned runs are charged to the pitcher — runs that scored through hits, walks and the like. Unearned runs are those that only scored because of a fielding error or passed ball. The official scorer reconstructs the inning without the mistakes to decide which runs are earned.
How do outs convert to innings pitched?+
Each out is one-third of an inning. So 6 innings and 1 out is written 6.1 and equals 6.333 innings, while 6 innings and 2 outs is 6.2 and equals 6.667. The '.1' and '.2' are outs, not tenths — a common source of miscalculation.
Can ERA be infinite?+
Yes. If a pitcher allows one or more earned runs without recording a single out, ERA is mathematically infinite because you would be dividing by zero innings. Box scores usually show this as 'INF' or a blank until the pitcher records an out.
Does ERA work the same way in softball?+
The method is the same, but fastpitch softball multiplies by 7 rather than 9 because a regulation game is seven innings: ERA = (7 × Earned Runs) ÷ Innings Pitched. Adjust the multiplier to match the game length you are scoring.
Why is ERA multiplied by nine?+
Because a standard MLB game is nine innings. Multiplying by nine normalises earned runs to a full-game rate, so a reliever who threw two innings and a starter who threw seven can be compared on the same per-game basis.
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Estimates & assumptions
- ERA uses the standard definition ERA = (9 × earned runs) ÷ innings pitched, per the MLB glossary.
- Whether a run is earned or unearned is decided by the official scorer; this tool takes earned runs as an input and does not judge scoring decisions.
- The 9-inning multiplier reflects baseball; use 7 for fastpitch softball or adjust for other formats.
- ERA is one measure of pitching and is most meaningful over a reasonable number of innings, not a single short appearance.
For entertainment and statistical use. Official statistics are maintained by the relevant league and its scorers.