Table of Contents
What is ERA?
Earned Run Average (ERA) is the most widely used statistic for evaluating pitching performance in baseball. It measures the average number of earned runs a pitcher allows per nine innings pitched. Earned runs exclude runs scored due to fielding errors, passed balls, or other defensive mistakes. ERA was first introduced in the early 1900s and remains the primary metric for comparing pitchers across different eras and leagues.
A lower ERA indicates better pitching performance. The league-average ERA in Major League Baseball has varied historically from about 2.5 in the dead-ball era to around 4.5 in high-offense periods. In the modern game, a starting pitcher with an ERA under 3.50 is considered very good, while anything under 2.50 is elite.
ERA Formula
When counting innings pitched, partial innings are expressed in thirds. So 6.1 means 6 and 1/3 innings, and 6.2 means 6 and 2/3 innings. This calculator handles decimal input directly for simplicity.
ERA Benchmarks
| ERA Range | Rating | Description |
|---|---|---|
| Under 2.00 | Elite / Cy Young | Historically dominant season |
| 2.00 - 3.00 | Excellent | All-Star caliber pitcher |
| 3.00 - 3.75 | Above Average | Quality starter |
| 3.75 - 4.50 | Average | Solid major leaguer |
| 4.50 - 5.50 | Below Average | Back-end starter or long relief |
| Over 5.50 | Poor | Replacement level |
ERA in Context
- ERA+ (adjusted ERA): Normalizes ERA to league average and park factors. 100 is league average; higher is better.
- Park effects: Coors Field inflates ERA by 10-15% due to altitude and thin air.
- Run environment: A 3.50 ERA was average in 2000 but excellent in 1968.
- Unearned runs: ERA does not include runs caused by errors, which can mask poor defense.
Frequently Asked Questions
What is a good ERA in MLB?
In modern MLB, a starting pitcher ERA under 3.50 is considered good, under 3.00 is excellent, and under 2.50 is elite. Relief pitchers typically have lower ERAs. The league-wide average ERA hovers around 4.00-4.50.
Why is ERA not a perfect stat?
ERA depends on the official scorer's judgment of errors, is affected by team defense quality, and does not account for park factors. Metrics like FIP (Fielding Independent Pitching) attempt to isolate what the pitcher controls: strikeouts, walks, hit batters, and home runs.
How do partial innings work?
If a pitcher records one out in an inning, that counts as 0.1 innings (one-third). Two outs is 0.2 innings (two-thirds). So 6.1 innings equals 6.333 in decimal form for calculation purposes.