Baseball ERA Calculator Formula

Understand the math behind the baseball era calculator. Each variable explained with a worked example.

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Formulas Used

Earned Run Average

era = earned_runs * 9 / innings_pitched

Earned Runs per Inning

runs_per_inning = earned_runs / innings_pitched

Variables

VariableDescriptionDefault
earned_runsEarned Runs Allowed35
innings_pitchedInnings Pitched100

How It Works

Earned Run Average (ERA)

ERA is the average number of earned runs a pitcher allows per nine innings. It is the most traditional measure of pitching effectiveness.

Formula

ERA = (Earned Runs / Innings Pitched) x 9

Only earned runs count (errors by fielders are excluded). A lower ERA is better. In modern MLB, an ERA below 3.00 is excellent, 3.00-4.00 is above average, and above 5.00 is poor.

Worked Example

A pitcher allows 35 earned runs in 100 innings.

earned_runs = 35innings_pitched = 100
  1. 01ERA = (35 / 100) x 9 = 0.35 x 9 = 3.15
  2. 02This is an above-average ERA in modern baseball

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