What Does ERA Mean in Baseball?
ERA — earned run average — is the classic measure of a pitcher's run prevention. It scales the earned runs a pitcher allows to a full game, so a starter and a reliever can be compared on the same footing.
What ERA measures
ERA estimates how many earned runs a pitcher would give up over a complete game if they pitched the whole thing at their current rate. Lower is better. Because it is per-game rather than per-season, it lets you compare pitchers who have thrown very different numbers of innings.
How to calculate ERA by hand
Multiply earned runs by the number of innings in a full game (9 for MLB), then divide by innings pitched. A pitcher with 22 earned runs over 68⅓ innings has an ERA of (22 × 9) ÷ 68.33 = 2.90. Remember that innings pitched use baseball notation: 68.1 means 68 and one out, or 68⅓ innings, which the calculator handles by working in thirds.
Earned versus unearned runs
Only earned runs count. If a runner reaches on an error and later scores, that run is unearned and excluded from ERA. The official scorer reconstructs the inning as if the error never happened to decide which runs were earned — a nuance that can make ERA slightly forgiving toward pitchers with shaky defenses behind them.
What is a good ERA at each level?
- MLB: sub-3.00 is ace territory, around 4.00 is average, 4.50+ is below average.
- College: aluminum-era offense pushes ERAs higher; a sub-3.50 ERA is strong.
- High school: wide talent gaps make ERA noisy; compare within a conference.
Limitations
ERA blends pitching and defense: a great defense suppresses runs a pitcher gets credit for, and a poor one inflates them. It also depends on the official scorer's error judgments. Fielding-independent stats like FIP strip defense out to isolate what the pitcher truly controls.