Earned run average

In baseball statistics, earned run average (ERA) is the average of earned runs allowed by a pitcher per nine innings pitched (i.e. the traditional length of a game). It is determined by dividing the number of earned runs allowed by the number of innings pitched and multiplying by nine. Thus, a lower ERA is better. Runs resulting from passed balls or defensive errors (including pitchers' defensive errors) are recorded as unearned runs and omitted from ERA calculations.

${\displaystyle {\text{ERA}}=9\times {\frac {\text{earned runs allowed}}{\text{innings pitched}}}}$