The number of runs earned divided by the total of innings pitched divided by 9. It's the number of earned runs allowed by the pitcher for each nine innings that they've pitched.

The number of earned runs a pitcher allows, multiplied by nine and divided by the official number of innings pitched. FLD

The average numbers of earned runs scored on a pitcher for a full nine-inning game. Refer to the statistics page for the proper formula to calculate this statistic.

Calculated as earned runs times nine divided by innings pitched. Introduced as an official stat in the NL in 1912 and in the AL in 1913.

The number of earned runs (runs scored without the benefit of an error) that pitcher allows, multiplied by nine (the number of innings in a regulation game) and divided by the actual number of innings pitched. Ex. Pitcher allows 5 earned runs in 6 innings. ERA = 5 X 9 = 45 / 6 = 7.50 ERA.