Earned Run Average (ERA) is one of the most common statistics used in comparing one pitcher to another; kind of like a batting average for pitchers. ERA is the number of runs that a pitcher would give up (on average, of course) throughout one complete game.
We calculate ERA by dividing the number of earned runs given up by the number of innings pitched, then multiplying this total by nine. We round the total off to two decimal places.
9 * (ER / IP) = ERA
For example, Cubs’ pitcher Paul Minner gave up 96 earned runs in 218 innings in 1954. 96 / 218 = .4403 * 9 = 3.9633. So Paul’s ERA was 3.96 for the season. Generally pitchers who keep their ERA under 3 are considered the top in the game.