Baseball ERA Calculator
Earned runs and innings to ERA and ERA+.
What it does
Earned run average compresses a season into nine innings: runs allowed per full game pitched. ERA+ then grades against league average with 100 as par. Two numbers frame every ace debate.
The tool above divides earned runs times nine by innings in baseball thirds notation, then scores ERA+ against league average. A 2.00 ERA in a 4.00 league reads 200: twice as good as average.
Major-league record keepers with sabermetric references define both the earned-run rules and the plus statistic. Unearned runs never count, thirds always convert, and park effects sit outside this unadjusted version.
Read ERA with company. Defense, parks, catchers, and inherited runners all tint runs allowed, so pair ERA+ with WHIP and strikeout rates before ranking pitchers.
How to use
- Enter earned runs allowed.
- Enter innings in baseball notation.
- Enter league ERA.
- Read ERA to two decimals.
- Read ERA+ against 100 average.
- Pair with WHIP and strikeouts.
Formula
- ER
- Runs without fielding errors.
- IP
- Innings pitched in baseball notation.
- league ERA
- League average ERA same season.
Innings use baseball thirds: .1 is one out, .2 two outs. ERA+ here is unadjusted for park; official versions add park factors. Only digits 0-2 may follow the decimal point.
Worked example
Example: 12 ER in 54 IP
12 earned runs in 54 innings, league ERA 4.00.
- Pitcher allows 12 earned runs over 54 innings.
- ERA: 12 x 9 / 54 = 2.
- League ERA is 4.00.
- ERA+: 100 x 4.00 / 2 = 200.
- 200 ERA+ means twice as good as average.
Reference table
| ERA+ | Meaning | Note |
|---|---|---|
| Under 100 | Below average | Trade candidate |
| 100 | League average | Par |
| 125 to 150 | Very good | All-Star fringe |
| 150 to 200 | Elite | Cy Young zone |
| Over 200 | Historic | Rare air |
Limits
- Unadjusted for park effects.
- Needs official earned/unearned splits.
- Small samples swing wildly.
- Defense tints every ERA.
Common mistakes
- Counting unearned runs.
- Reading decimals as tenths.
- Comparing across eras directly.
- Ignoring park effects.
- Judging relievers by ERA alone.
Try it yourself
Quick checks. Answers sit tucked under each question.
20 ER in 60 IP, league 4.00?
ERA is 20 x 9 / 60 = 3. ERA+ is 100 x 4 / 3 = 133. Better than league.
7 ER in 21.1 IP, league 4.00?
21.1 means 21 and one third (21.333). ERA is 7 x 9 / 21.333 = 2.95. ERA+ is 135.
Questions
How is ERA figured?
Earned runs times nine divided by innings pitched. Unearned runs from errors never count, which is why official scorers matter as much as pitchers.
What does 54.1 innings mean?
Baseball notation: .1 means one out, .2 two outs. So 54.0 is 54 full innings while 54.1 adds one out. The tool converts thirds automatically.
What is ERA+?
100 times league ERA over pitcher ERA, park-adjusted in official versions. 100 is average, 150 is excellent, 200 is historic. Above 100 always beats average.
Does ERA measure skill alone?
No. Team defense, ballparks, catchers, and luck shape runs allowed. ERA+ adjusts for league and park; FIP strips fielding further.
Why do reliever ERAs swing wildly?
Relievers inherit runners and leave mid-inning, so thirds matter enormously. One out changes small-sample ERAs by runs.
What pairs with ERA?
Quality starts, WHIP, strikeout-minus-walk rates, and ERA+ together. Single numbers lie; trios tell truth about pitchers.