Earned Run Average Calculator
Earned run average (ERA) is baseball's most familiar measure of how well a pitcher prevents runs. It expresses the number of earned runs a pitcher allows over a full nine-inning game, which is the standard length of a game, so that pitchers who threw very different numbers of innings can be compared on an even footing. The calculation is simple: take the earned runs the pitcher has allowed, multiply by nine, and divide by the innings pitched. Multiplying by nine is what rescales the figure to a whole game. Only earned runs count, runs that scored because of a fielding error or passed ball are unearned and excluded, which is what makes ERA a measure of the pitcher's own work rather than the defense behind them. A lower ERA is better: under 3.00 is excellent and above 5.00 is poor, though the league average drifts from season to season. This calculator applies the standard formula exactly: enter earned runs and innings pitched, remembering to write partial innings as decimals, and it returns the ERA. Every figure here is computed deterministically from the formula shown below, with a worked example that reconciles exactly to the calculator so you can follow each step.
Earned run average is earned runs scaled to a nine-inning game: ERA = 9 x earned runs / innings pitched. A pitcher with 30 earned runs over 75 innings has an ERA of 3.60. Lower is better.
Earned run average formula
ERA = 9 x ER / IP
ER = earned runs allowed
IP = innings pitched (partial innings as decimals)
9 = innings in a standard game
Multiplying earned runs by nine and dividing by innings pitched scales run prevention to a full game, so a starter and a reliever can be compared on the same per-game basis.
Worked example
A pitcher has allowed 30 earned runs across 75 innings pitched.
- Multiply earned runs by nine: 30 x 9 = 270.
- Divide by innings pitched: 270 / 75.
- ERA = 3.60.
The earned run average is 3.60. These are the calculator's default inputs, so the result above matches the widget exactly.
How ERA is generally read
| ERA range | General assessment |
|---|---|
| Below 2.00 | Outstanding |
| 2.00 to 3.00 | Excellent |
| 3.00 to 4.00 | Above average |
| 4.00 to 5.00 | Average to below average |
| Above 5.00 | Poor |
General ranges; compare against the same season's league average for context.
ERA calculator: frequently asked questions
What is earned run average (ERA)?
Earned run average is the average number of earned runs a pitcher allows per nine innings, the length of a standard baseball game. It is the most familiar single measure of a pitcher's run prevention. A lower ERA is better: an ERA under 3.00 is generally excellent, while an ERA above 5.00 is poor.
How is ERA calculated?
ERA equals earned runs allowed, multiplied by nine, divided by innings pitched. Multiplying by nine scales the result to a full nine-inning game so that pitchers who threw different numbers of innings can be compared on the same basis. Only earned runs count; runs that score because of fielding errors are excluded.
What counts as an earned run?
An earned run is a run charged to the pitcher that scored without the benefit of a fielding error or a passed ball. If a run only scored because of a defensive mistake, it is unearned and does not count toward ERA. This is why ERA isolates the pitcher's own contribution from the defense behind them.
How are partial innings entered?
Innings pitched are recorded in thirds, because there are three outs per inning. One out is one third of an inning, written as .1, and two outs is two thirds, written as .2. For this calculator, convert thirds to a decimal first: 75 and one third innings is entered as 75.33, and 75 and two thirds as 75.67.
Is a lower or higher ERA better?
Lower is better. ERA measures runs allowed, so the fewer earned runs a pitcher gives up per nine innings, the more effective they are at preventing the other team from scoring. League-average ERA shifts from season to season, so it is most useful when compared against the same season's league average.
Official sources
- Public health and sport participation context: US Centers for Disease Control and Prevention (CDC). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.