ERA (Earned Run Average)

ERA stands for Earned Run Average, calculated as the average number of earned runs a pitcher allows per nine innings pitched. It's one of the most important statistics for evaluating pitcher performance.

The ERA Formula

ERA = (Earned Runs × 9) ÷ Innings Pitched

For example, if a pitcher allows 30 earned runs over 90 innings:

• 30 × 9 = 270
• 270 ÷ 90 = 3.00 ERA

What Counts as an "Earned Run"?

An earned run is a run that scores without the help of defensive errors or passed balls. If a runner reaches on an error and later scores, that's an unearned run, it doesn't count against the ERA.

What's a Good ERA?

ERA Range	Rating
Below 3.00	Elite
3.00-3.50	Excellent
3.50-4.00	Above Average
4.00-4.50	Average
4.50-5.00	Below Average
Above 5.00	Poor

Note: These benchmarks vary by era and league.

ERA in Context

ERA has limitations:

• Doesn't account for ballpark factors
• Ignores quality of defense behind the pitcher
• Unearned runs can still affect games
• Modern metrics (FIP, xERA) provide more context

All-Time ERA Leaders

• Ed Walsh: 1.82 career ERA (deadball era)
• Mariano Rivera: 2.21 career ERA (modern era)
• Clayton Kershaw: Among the best active pitchers

ERA+

ERA+ adjusts for ballpark and league, where 100 is average. An ERA+ of 150 means the pitcher was 50% better than average.