acalculator

What is my ERA?

Enter the earned runs and the innings pitched as a box score writes them. The ERA calculator scales the runs to a nine-inning game.

Your numbers

Write 6⅓ innings as 6.1 and 6⅔ innings as 6.2.
ERA
2.49

The ERA is 2.49 (earned runs 25, innings pitched 90⅓).

Innings pitched
90⅓
Outs recorded
271
Earned runs per inning
0.277

ERA: 2.49. The ERA is 2.49 (earned runs 25, innings pitched 90⅓).

How to calculate

Computes a pitcher’s earned run average (ERA), the earned runs allowed per nine innings, from earned runs and innings pitched in box-score notation (6.2 is 6⅔ innings).

Example with the default inputs (Earned runs 25, Innings pitched 90.1, Innings in a game 9): The ERA is 2.49 (earned runs 25, innings pitched 90⅓).

Method: ERA = earned runs × innings in a game ÷ innings pitched, with innings pitched in thirds (outs ÷ 3), so 6.2 is 20 outs, 6⅔ innings.

  • Innings pitched use box-score notation: the digit after the point counts outs (.1 is one out, .2 is two outs). Any other decimal has no answer.
  • The ERA is scaled to 9 innings unless you change Innings in a game (a league of 7-inning games may use 7).
  • Earned runs are whole numbers from 0 to 100,000; innings pitched are up to 100,000.
  • With earned runs but no outs recorded the ERA is infinite, and with no outs and no runs there is none; both give no answer.
  • The ERA is shown to two decimal places, rounded half up from the exact fraction.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Earned runs 3, Innings pitched 4, Innings in a game 9 gives ERA 6.75, Innings pitched 4, Outs recorded 12, Earned runs per inning 0.75.Source: Baseball-Reference, Earned Run Average glossary (3 ÷ 4 × 9 = 6.75). https://www.baseball-reference.com/glossary/earned-run-average/
  2. Earned runs 2,147, Innings pitched 7,356, Innings in a game 9 gives ERA 2.63, Outs recorded 22,068.Source: Baseball-Reference, Earned Run Average glossary (2,147 ÷ 7,356 × 9, shown as 2.63). https://www.baseball-reference.com/glossary/earned-run-average/
  3. Earned runs 3, Innings pitched 9.1, Innings in a game 9 gives ERA 2.89, Innings pitched 9⅓, Outs recorded 28.Source: 3 × 9 × 3 ÷ 28 = 81/28 = 2.89 (formula from Baseball-Reference, https://www.baseball-reference.com/glossary/earned-run-average/)
  4. Earned runs 58, Innings pitched 180.2, Innings in a game 9 gives ERA 2.89, Innings pitched 180⅔, Outs recorded 542.Source: 58 × 9 × 3 ÷ 542 = 783/271 = 2.89 (formula from Baseball-Reference, https://www.baseball-reference.com/glossary/earned-run-average/)
  5. Earned runs 10, Innings pitched 35, Innings in a game 7 gives ERA 2.00, Earned runs per inning 0.285714.
  6. Earned runs 0, Innings pitched 0.2, Innings in a game 9 gives ERA 0.00, Innings pitched ⅔, Outs recorded 2.

How it works

The earned run average is the number of earned runs a pitcher allows per nine innings:

ERA = earned runs × innings in a game ÷ innings pitched

Innings in a game is 9 unless you change it.

Innings pitched in box-score notation

Box scores write a partial inning by its outs. The digit after the point is the number of outs, not a decimal fraction:

  • 6 or 6.0 is 6 innings (18 outs)
  • 6.1 is 6⅓ innings (19 outs)
  • 6.2 is 6⅔ innings (20 outs)

The calculator counts the innings in outs: outs = 3 × whole innings + the digit after the point, and innings pitched = outs ÷ 3. So the ERA is

ERA = earned runs × innings in a game × 3 ÷ outs

Rules

  • The part after the point must be .0, .1 or .2 (trailing zeros are fine, so 6.10 is 6.1). Any other value, such as 6.3 or 6.25, gives no answer: "Write innings pitched with .1 for one out and .2 for two outs (6.2 is 6⅔ innings); a third out makes a whole inning."
  • Earned runs are whole numbers from 0 to 100,000. Innings pitched are from 0 to 100,000. Innings in a game is a whole number from 1 to 12.
  • With 0 innings pitched and 0 earned runs there is no ERA: "Enter the innings pitched: with no outs recorded there is no ERA."
  • With 0 innings pitched and earned runs above 0 the ERA is infinite: "The ERA is infinite: earned runs were charged before the pitcher recorded an out."

What the calculator shows

  • ERA: the exact fraction above, rounded half up to hundredths and always written with exactly two decimal places, as box scores print it: 2.00, 0.00, 4.50, 6.75, 2.89. It is plain text: digits, a point, two digits, with no thousands separators.
  • Innings pitched: the whole innings followed by ⅓ or ⅔ for a partial inning (6⅔; ⅔ alone for two outs; 4 for exactly four innings).
  • Outs recorded: 3 × whole innings + partial outs.
  • Earned runs per inning: earned runs × 3 ÷ outs, rounded half up to at most three decimal places, without trailing zeros.

Worked examples by hand

3 earned runs in 4 innings (Paul Skenes’s first start, from Baseball-Reference): 4 innings is 12 outs. ERA = 3 × 9 × 3 ÷ 12 = 81 ÷ 12 = 6.75. Earned runs per inning: 3 × 3 ÷ 12 = 0.75.

2,147 earned runs in 7,356 innings (Cy Young’s career): ERA = 2,147 × 9 ÷ 7,356 = 19,323 ÷ 7,356 = 2.62684, shown as 2.63.

3 earned runs in 9.1 innings: 9.1 is 9⅓ innings, 28 outs. ERA = 3 × 9 × 3 ÷ 28 = 81 ÷ 28 = 2.892857, shown as 2.89.

58 earned runs in 180.2 innings: 180.2 is 180⅔ innings, 542 outs. ERA = 58 × 9 × 3 ÷ 542 = 1,566 ÷ 542 = 783 ÷ 271 = 2.889299, shown as 2.89.

A 7-inning league, 10 earned runs in 35 innings: ERA = 10 × 7 ÷ 35 = 2, written 2.00. Earned runs per inning: 10 ÷ 35 = 0.286.

No runs in 0.2 innings: 2 outs, ⅔ of an inning. ERA = 0 × 27 ÷ 2 = 0, written 0.00.

Other questions people ask

How do I calculate ERA?

Multiply the earned runs by 9 and divide by the innings pitched. A pitcher who allows 3 earned runs in 4 innings has an ERA of 3 × 9 ÷ 4 = 6.75.

What do innings like 6.1 and 6.2 mean?

Box scores count a partial inning in outs: 6.1 means 6 innings and 1 out (6⅓ innings) and 6.2 means 6 innings and 2 outs (6⅔). The calculator reads them that way, so 6.2 is never treated as 6.2 innings. A third out makes a whole inning, so 6.3 is not used.

What is a good ERA?

Lower is better, because ERA counts the runs a pitcher allows. Compare an ERA with the league average for the same league and season, which stat sites such as Baseball-Reference publish every year: a pitcher well below the average had a strong season.

What is the difference between a run and an earned run?

An earned run is a run the pitcher is charged with because it scored without help from a fielding error or a passed ball. The official scorer decides which runs are earned. Only earned runs go into ERA.

Can an ERA be infinite?

Yes. A pitcher who gives up an earned run before recording a single out has 0 innings pitched, so the ERA would divide by zero. Stat pages print it as ∞; the calculator says it is infinite and shows no number.

How is ERA calculated for 7-inning games?

Set Innings in a game to 7. The formula becomes earned runs × 7 ÷ innings pitched, so 10 earned runs in 35 innings is an ERA of 2.00. Leagues differ, so check which length your league uses.