Definition – What is Earned Run Average?
ERA is the number of runs a pitcher allows for every 9 innings of play (7 innings for some leagues). The lower the number, the fewer runs the pitcher allows.
ERA is adjusted to the number of innings a pitcher has played. It is seen as more accurate than a win/loss ratio.
A pitcher with an ERA of 3.00 typically allows 3 runs for every 9 innings of play. (If the pitcher is in a league with 7 regulation innings, they would allow 3 runs for every 7 innings of play.
Formula – How to calculate ERA
ERA = (Earned Runs Allowed ÷ Innings Pitched) x Innings in a Regulation Game
Each out that is pitched counts as 1/3 of an inning.
Most professional level games are nine innings. Softball games are typically seven innings, and little league games are often six or seven innings.
An ERA is listed to 2 decimal points.
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
Sources and more 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.