Baseball ERA Calculator

2 earned runs in 6 innings is a 3.00 ERA; 1 in 7 innings is 1.29

ERA, short for earned run average, tells you how many earned runs a pitcher allows for every nine innings. Rule 9.21(e) of MLB's 2026 Official Baseball Rules says to multiply the earned runs charged to the pitcher by 9 and divide by the innings he pitched, including fractions of an inning: ERA = earned runs × 9 ÷ innings pitched. Two earned runs over six innings make 2 × 9 ÷ 6 = 3.00, and one earned run over seven innings makes 1 × 9 ÷ 7 = 1.29.

A full season works the same way. In 2026 Jacob Misiorowski of the Milwaukee Brewers pitched 174⅔ innings (174.2 in a box score) in 30 regular-season games and allowed 35 earned runs. 35 × 9 ÷ 174⅔ = 1.80, the lowest ERA among the 46 pitchers who threw enough innings to qualify, while the MLB average that year was 4.17. The calculator above opens with those 30 games, one row per game.

Why ERA matters and when to calculate it

The MLB Glossary credits the statistician and writer Henry Chadwick with inventing ERA in the mid-to-late 19th century, because he felt a win-loss record did not go far enough in identifying a good pitcher. The stat caught on in the 20th century as relief pitchers became more common, since a starter could pitch a great game and still miss out on the win if his bullpen did not hold the lead. The glossary calls ERA the most commonly accepted statistical tool for evaluating pitchers. Typical reasons to work it out yourself:

• Turning the game-by-game lines you kept for a rec league, high school or college team into a season ERA
• Checking in mid-season how many scoreless innings it would take to reach a target ERA
• Seeing where a pitcher you follow stands against this year's league average and the qualified pitchers
• Re-reading a record on a 7-inning or 6-inning basis for a league that plays shorter games

How to use the calculator

1. Enter one game per row. Type innings the way a box score shows them, such as 6.2 (6⅔ and 6 2/3 work too). A blank earned-runs box counts as 0. If you only have season totals, fill in just the first row.
2. Press Enter in the last box to jump to the next row, or press Add game when you run out of empty rows.
3. Pick a comparison league (KBO, MLB or NPB) to see its 2026 average, the league index and where the record would rank among that league's qualified pitchers.
4. For a league that plays 7-inning games, set Innings basis to 7 innings. League comparisons appear only on the 9-inning basis.
5. Type a value into Target ERA under the chart to see how many scoreless innings it would take to get there or, if you are already below it, how many more earned runs you could allow.
6. Use Load a record to bring in any 2026 qualified pitcher's season totals or one of three game-by-game examples: Misiorowski, Yoshinobu Yamamoto and Gwak Been of the KBO's Doosan Bears.

How ERA is calculated

MLB's 2026 Official Baseball Rules and the KBO's 2026 rulebook use the same formula in Rule 9.21. The MLB rule divides by the innings pitched "including fractions of an inning", and a note in the KBO rulebook says the KBO also counts the ⅓ and ⅔ parts of an inning.

• ERA = earned runs × 9 ÷ innings pitched
• Innings pitched = outs recorded ÷ 3, so 5.2 in a box score means 5⅔ innings, or 17 outs
• For several games, add up the innings (outs) and the earned runs first, then divide once. Averaging each game's ERA gives the wrong answer.
• On a different innings basis, multiply by that number instead of 9 (7-inning basis = earned runs × 7 ÷ innings pitched).
• The displayed value is rounded to two decimal places. A note to Rule 9.21 in Japan's NPB rules likewise says ERA is worked out to the third decimal place and then rounded.

Why 5.1 and 5.2 are not decimals

In a box score, 5.1 and 5.2 are not decimal numbers. They are shorthand for five innings plus one or two outs. The MLB Glossary explains that an inning has three outs, so each out is one-third of an inning pitched. Pickoffs and caught stealing count, and a double play is worth two-thirds of an inning. When a batter reaches on an error, the pitcher gets no third of an inning, because no out was recorded.

Treat 5.2 as an ordinary decimal and 2 × 9 ÷ 5.2 gives 3.46 instead of the correct 3.18. The calculator also reads a value written as 174 2/3 as 174⅔ innings, and it flags a last digit of 3 or more (such as 5.3) as an error, since that is not a valid innings figure.

Earned runs are not the same as runs allowed

ERA counts earned runs, not every run a pitcher gives up. Rule 9.16 defines an earned run as a run for which the pitcher is held accountable. The official scorer reconstructs the inning without the errors and passed balls and counts only the runs that would still have scored. When in doubt, the pitcher gets the benefit.

• Earned: runs that score with the help of hits, sacrifice bunts, a sacrifice fly, stolen bases, walks (intentional walks included), hit batters, balks or wild pitches. The rule calls a wild pitch "solely the pitcher's fault".
• Not earned: a run by a runner who reached first base on a fielding error, interference or obstruction, a run by a runner who would have been put out with errorless play, and a run that would not have scored without an error or a passed ball.
• Pitching changes: when a pitcher leaves with runners on base, he is charged with the runs scored afterward up to the number of runners he left on base (Rule 9.16(g)). The rule's comment says it counts the number of runners, not the individual runners.

2026 league averages and qualified pitchers

The same ERA reads differently from league to league. The table below uses each league's official regular-season pitching totals (earned runs × 27 ÷ outs) and its list of qualified pitchers. The calculator's league index sets the league average at 100 (league average ÷ this ERA × 100). Unlike ERA+ in the MLB Glossary, it makes no ballpark adjustment.

All three leagues had a higher average than in 2025, though MLB barely moved (4.15 to 4.17). In the NPB, 17 of the 22 qualified pitchers finished under 3.00, so a 3.00 ERA lands near the bottom of that list. In the KBO, where Gwak Been was the only qualified pitcher under 3.00, the same 3.00 would rank right behind him. Most qualified pitchers had a lower ERA than their league average (16 of 18 in the KBO, 36 of 46 in MLB and 20 of 22 in the NPB), so read a rank together with the average.

Each earned run weighs less as the innings pile up

Because ERA divides earned runs by innings, a single run moves it a lot while the innings are few. Misiorowski opened 2026 with 5 innings and 1 earned run, a 1.80 ERA. After his fourth game it had climbed to 3.32, its high point for the season. His 14th game, 9 innings without an earned run, brought it down to 1.34, its low point, and he finished the season back at 1.80. Even late in the year a rough outing showed: 5 earned runs in 4 innings in his 26th game lifted his ERA from 1.73 to 1.97. Over the 30 games, 18 (60%) met the MLB Glossary's quality-start line of at least six innings and three or fewer earned runs, and 12 had no earned runs at all.

In the calculator's chart, the dark line is this running ERA. Press Flatten and every bar moves to the same height, which equals the season ERA, because each bar's area (innings × game ERA) is earned runs × 9.

Scoreless innings needed to reach a target ERA

Adding scoreless innings leaves the earned runs unchanged and only makes the denominator bigger. So the innings you need for a target ERA are earned runs × 9 ÷ target, and subtracting the innings already pitched gives the scoreless innings still to go. The calculator finds the smallest number of outs at which the displayed ERA (rounded to two decimals) reaches the target or drops below it.

• Misiorowski, 1.80 → 1.50: 34⅔ scoreless innings (104 outs)
• Yoshinobu Yamamoto (LAD), 2026 regular season with 185 innings and 52 earned runs, 2.53 → 2.00: 48⅔ scoreless innings (146 outs)
• If the record is already under the target, the calculator shows the reverse: how many more earned runs could be allowed in the same innings without going over. Against the default target of 3.00, Misiorowski had room for 23 more earned runs.

Common mistakes

• Using runs instead of earned runs: unearned runs push the ERA higher than it really is. Use the ER column of the box score.
• Averaging each game's ERA: a 1-inning game with 1 earned run (9.00) and a 5-inning game with 1 earned run (1.80) do not average out to the right answer. Add them up first: 2 earned runs in 6 innings is 2 × 9 ÷ 6 = 3.00.
• Earned runs with no outs: there are no innings to divide by, so there is no number to show. The calculator displays infinity (∞).
• Comparing a 7-inning-basis ERA with a 9-inning league average: a smaller basis shrinks the number (Misiorowski: 1.80 on a 9-inning basis, 1.40 on a 7-inning basis).
• Comparing a short sample with the league leader: the rank is only a reference point. With few innings, each run weighs more and the ERA swings widely.

Limitations

• As the MLB Glossary points out, ERA takes defensive mistakes into account but not great defensive plays, so a pitcher with an average defense is at a disadvantage to one with a great defense. The glossary adds that league differences, such as whether a designated hitter is used, and the ballpark itself can affect ERA. If you want to focus on what the pitcher controls, check FIP alongside ERA.
• The glossary also says ERA is less effective for relief pitchers, who often pitch only fractions of an inning and leave their ERA in the hands of other relievers, and that relievers generally have lower ERAs than starters.
• The league index has no park adjustment, so it can differ from the ERA+ shown on stats sites.
• League averages and qualified-pitcher lists are official figures for the 2026 regular season and do not include the postseason.

As of The formula and rules were checked on 2026-10-23 against the original texts of MLB's 2026 Official Baseball Rules, the KBO's 2026 rulebook and the NPB's Official Baseball Rules, and the definitions on 2026-10-24 against the MLB Glossary. League averages and qualified pitchers come from the 2026 and 2025 regular-season records of the KBO record site, MLB (Stats API) and the NPB, and the game-by-game examples from KBO and MLB Stats API game logs downloaded on 2026-10-24.

Sources

• 01MLB — 2026 Official Baseball Rules (PDF)9.16 earned runs (inning reconstructed without errors and passed balls, wild pitches, pitching changes), 9.21(e) ERA formula and the 9⅓ innings, 3 earned runs = 2.89 example, 9.22(b) qualifying innings (161⅔ innings does not qualify)
• 02KBO — 2026 Baseball Rules (PDF, Korean)9.21(e) earned run average, note that the KBO counts ⅓ and ⅔ innings, 9.22(b) note: at least as many innings as the team's games in the season
• 03NPB — Official Baseball Rules 9.00 (PDF, Japanese)9.21(e) ERA, note: worked out to the third decimal place and rounded
• 04MLB Glossary — Earned Run Average (ERA)Definition, formula 9 × earned runs ÷ innings pitched, effects of defense, league and ballpark, relief pitchers, Henry Chadwick and win-loss records
• 05MLB Glossary — ERA+League average = 100, park-adjusted league ERA × 100 ÷ ERA
• 06MLB Glossary — Innings Pitched (IP)One out = ⅓ inning, pickoffs and caught stealing count, double play = ⅔ inning, no innings for a batter reaching on an error
• 07MLB Glossary — Quality Start (QS)A start of at least 6 innings with 3 or fewer earned runs
• 08KBO record site — team pitching2026 regular season: 12,760⅔ innings, 6,606 earned runs. 2025: 12,773⅔ innings, 6,115. The 18 qualified pitchers come from the player records on the same site
• 09KBO record site — Gwak Been game log2026 regular season: 27 games, 161 innings, 40 earned runs (matches the qualified-pitcher total)
• 10MLB Stats API — 2026 team pitching43,079⅔ innings, 19,966 earned runs. 2025: 43,075 innings, 19,869. The 46 qualified pitchers and the Misiorowski and Yamamoto game logs come from the same API
• 11NPB — 2026 team pitching (Japanese)Central and Pacific leagues: 15,276 innings, 5,618 earned runs. 2025: 15,392⅓ innings, 5,141. The 22 pitchers with qualifying innings come from the pit_c and pit_p pages

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