ERA Calculator (Baseball)

Earned Run Average is the standard shorthand for how effective a pitcher has been, and this tool computes it from the runs and innings you supply. Because ERA expresses the average number of earned runs a pitcher allows per nine innings, a lower figure means stronger performance. The calculator labels an ERA under 2.50 Excellent, 2.50 to 3.49 Good, 3.50 to 4.49 Average, and 4.50 or higher Poor.

The math behind the figure is short: divide earned runs by innings pitched, then multiply by 9. Earned runs are those a pitcher gives up without the help of a fielding error, so they isolate the pitcher's own responsibility. Innings pitched includes partial innings expressed as thirds, which is why a line like 5.1 innings means five and one-third innings rather than five and one-tenth.

The split between total runs and earned runs is the one detail worth getting right, because only earned runs belong in the calculation. Folding in unearned runs is the usual error, and it inflates the result past what the pitcher actually earned. Bear in mind as well that ERA is a rate, so over a handful of innings it swings wildly and tells you very little about true ability.