Baseball 101: Earned Run Average

A pitcher’s Earned Run Average (or ERA) is the average number of earned runs that a pitcher gives up per nine innings pitched (as the typical game lasts nine innings).

An earned run is a run that is not scored as the result of a defensive error, such as a fielding error or a passed ball.

A pitcher’s ERA is calculated by dividing the number of earned runs he has allowed by the number of innings he has pitched, then multiplying by nine.  For example, if a pitcher is charged with 21 earned runs over the course of 90 innings pitched, his ERA would be 2.10.

(21/90) x 9 = 2.1

An ERA under 3.00 is generally considered to be excellent.  The lower a pitcher’s ERA, the better.

The lowest all-time career ERA in baseball history was 1.82, by Ed Walsh, who pitched from 1904 to 1917.  The lowest career ERA during the live-ball era (that is, post-1920), belongs to Mariano Rivera, who pitched from 1995-2013 and posted an ERA of 2.21.

Ed Walsh, 1911 (Photo source: wikimedia.org)


3 Comments on “Baseball 101: Earned Run Average”

  1. steve says:

    As fascinating as BABIP and WAR and what not is, I still can’t shake ERA off my tongue. Kei Igawa will forever hold a career ERA of 6.66 in the MLB unless he jumps again form the Japanese League.

  2. crs268 says:

    What a bad ass picture! Great post too 🙂


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