ERA Calculator (Earned Run Average)

What is ERA (Earned Run Average)?

ERA, or Earned Run Average, is one of the core pitching statistics in baseball and softball. It estimates how many earned runs a pitcher would allow over a standard game length.

In Major League Baseball, a standard game is 9 innings, so ERA answers the question: “If this pitcher kept pitching like this, how many earned runs would they allow every 9 innings?”

ERA formula

For MLB and most professional leagues, innings per game = 9, so:

Handling innings and outs correctly

Innings pitched can be tricky because scoreboards often show thirds of an inning as .1 and .2, not true decimals:

• 7.0 = 7 full innings
• 7.1 = 7 innings + 1 out (7⅓ innings)
• 7.2 = 7 innings + 2 outs (7⅔ innings)

Our calculator lets you enter innings either in this scoreboard decimal format or as full innings + outs. Internally, we always convert to true fractional innings:

• 1 out = 1⁄3 inning ≈ 0.3333
• 2 outs = 2⁄3 inning ≈ 0.6667

Step-by-step ERA example

Suppose a pitcher has the following season line:

• Earned runs allowed: 20
• Innings pitched: 90.0
• League: standard 9-inning games

1. Convert innings pitched (already 90.0, so no change).
2. Multiply earned runs by innings per game: 20 × 9 = 180.
3. Divide by innings pitched: 180 ÷ 90 = 2.00.

The pitcher’s ERA is 2.00, which is excellent.

Example with partial innings

Now imagine a reliever with:

• Earned runs: 7
• Innings pitched: 12.2 (12 innings, 2 outs)

1. Convert 12.2 to true innings: 12 + 2⁄3 = 12.6667 innings.
2. Multiply earned runs by 9: 7 × 9 = 63.
3. Divide: 63 ÷ 12.6667 ≈ 4.97.

The reliever’s ERA is about 4.97.

What is a good ERA?

Ranges vary by era and league, but for modern MLB starting pitchers:

• Under 3.00 – Elite / Cy Young-level
• 3.00 – 3.75 – Very good
• 3.75 – 4.25 – Around league average
• 4.25 – 5.00 – Below average
• Above 5.00 – Poor

Relievers often have more volatile ERAs because they pitch fewer innings, so a single bad outing can move their ERA dramatically.

Limitations of ERA

ERA is useful but not perfect:

• It depends on defense behind the pitcher.
• It ignores unearned runs (runs scored after errors or passed balls).
• It doesn’t account for ballpark factors or league scoring environment.

For deeper analysis, advanced stats like FIP, xFIP, ERA+ and WAR adjust for some of these factors, but ERA remains the most familiar quick snapshot of a pitcher’s run prevention.

Frequently asked questions about ERA

Does ERA include unearned runs?

No. ERA includes only earned runs. If a run scores because of an error or passed ball, it is usually recorded as unearned and excluded from ERA.

Can ERA be negative?

In practice, no. ERA is based on runs allowed, which can’t be negative. A pitcher who hasn’t allowed any earned runs yet will have an ERA of 0.00.

How soon does ERA become meaningful?

ERA is very volatile over small samples. A single bad inning early in the season can inflate ERA for weeks. Many analysts prefer at least 50–70 innings before drawing strong conclusions.