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Earned run average (ERA) is one of the most important statistics used to evaluate pitchers in baseball and softball. It measures the average number of earned runs a pitcher allows per game. Earned runs are runs that score without the benefit of an error or a passed ball.

A lower ERA indicates a more effective pitcher. ERA allows you to compare pitchers regardless of how many innings they have pitched, making it a useful statistic for evaluating both starters and relievers.

ERA Formula

The ERA formula is earned runs times innings per game, divided by innings pitched:

\[ \text{ERA} = \frac{\text{earned runs} \times \text{innings per game}}{\text{innings pitched}} \]

Innings per game = 9 for baseball, 7 for softball, and 6 for Little League.

How to Calculate ERA

1. Count earned runs allowed
2. Count innings: full innings pitched plus partial innings
3. Divide [earned runs × innings per game] by innings pitched
4. Round to 2 decimal places

Earned runs do not include unearned runs caused by errors or passed balls.
Partial innings are the number of outs in an inning when the pitcher leaves the game. Each out recorded in an incomplete inning = ⅓ inning.

Decimal Innings Pitched Notation

In baseball statistics, innings pitched (IP) are recorded using a special notation where the decimal portion represents outs and not a true decimal amount. A pitcher credited with .1 IP means there was 1 out (⅓ inning) in the inning when the pitcher left the game. And .2 IP means there were 2 outs (⅔ inning) in the inning when the pitcher left the game. So 6.1 IP means the player pitched 6 full innings plus 1 out, when they left the game. This equals 6⅓ innings or 19 total outs. This calculator lets you select partial innings to avoid confusion with decimal notation inputs.

ERA Examples

Single-game example: A pitcher allows 3 earned runs in 6⅔ innings pitched in a 9-inning baseball game. Using the ERA formula:

\[ \text{ERA} = \frac{\text{earned runs} \times \text{innings per game}}{\text{innings pitched}} \]

• ERA = (3 × 9) ÷ 6 ⅔
• Convert ⅔ to a decimal: 2 ÷ 3 = 0.667, so IP = 6.667
• ERA = (3 × 9) ÷ 6.667
• ERA = 27 ÷ 6.667 = 4.05

Full-season example: A pitcher allows 65 earned runs in 200 innings pitched in 9-inning baseball.

• ERA = (65 × 9) ÷ 200
• ERA = 585 ÷ 200
• ERA = (65 × 9) ÷ 200 = 2.93 (rounded from 2.925)

References

• Major League Baseball. "Earned Run Average (ERA)." MLB.com Glossary. mlb.com/glossary/standard-stats/earned-run-average
• Major League Baseball. "Innings Pitched (IP)." MLB.com Glossary. mlb.com/glossary/standard-stats/innings-pitched
• Baseball Reference. "Earned Run Average (ERA)." baseball-reference.com/glossary/earned-run-average