Definition – What is Earned Run Average (ERA)?

The number of earned runs a pitcher gives up in a regulation game, which usually lasts nine innings (or seven innings in some leagues), is measured by the Earned Run Average (ERA). Better pitching performance is indicated by a lower ERA since it suggests that the pitcher gives up fewer runs on average.

ERA is a more accurate indicator of a pitcher’s effectiveness than a win/loss record since it accounts for the amount of innings pitched, which gives a fair judgment.

An ERA of 3.00, for instance, means that a pitcher allows roughly three earned runs every nine innings (or seven, depending on the league’s regulation length).

Example

If a pitcher has pitched 98 innings and 1 out and has allowed 28 Earned Runs, then:
ERA = (28 ÷ (98 + 1/3)) x 9
ERA = (28 ÷ 98.333) x 9
ERA = 0.28475 x 9
ERA = 2.5627
Therefore, the pitcher’s ERA is 2.56

Resources:

• Wikipedia – Earned Run Average and Earned Run.
• Glossary entries on ERA from Sporting Charts.
• ERA statistics from ESPN, NCAA, and Baseball-Reference (Career Leaders & Records).
• Rules on baseball and baseball statistics from Major League Baseball, NCAA (Baseball), NCAA (Softball), NCAA (Baseball and Softball), NFHS, and the International Baseball Federation.