ERA Calculator (Earned Run Average)
Calculate Earned Run Average (ERA) from earned runs and innings pitched, with correct handling of baseball innings notation (6.1 = 6⅓, 6.2 = 6⅔). Free.
ERA Calculator
Earned Run Average is baseball's classic measure of a pitcher: the number of earned runs they allow per nine innings. Enter the earned runs and innings pitched — using baseball's .1 / .2 notation for partial innings — to get the ERA.
Innings use baseball notation: .1 = one out (⅓), .2 = two outs (⅔). E.g. 180.2 = 180⅔ innings.
How to Use the ERA Calculator
Enter earned runs
Use earned runs, not total runs — runs that scored due to fielding errors or passed balls are "unearned" and don't count toward ERA. The official scorer makes that call; a box score lists ER separately.
Enter innings pitched
Use baseball notation: 180.0 is 180 innings, 180.1 adds one out (⅓ inning), 180.2 adds two outs (⅔). The tool converts the partial innings correctly — don't enter 180.33.
Read the ERA
The result is earned runs per nine innings. A starter's full-season ERA in the low 3.00s is very good; relievers and small samples swing more. Compare to the league average for the season to judge it fairly.
Pair it with FIP
ERA records the runs that actually scored, but it's influenced by defense and luck. For a defense-independent view of pitcher skill, compute FIP with our FIP calculator and compare the two.
ERA — Baseball's Oldest Pitching Yardstick
What ERA Measures and Why the "Earned" Matters
Earned Run Average dates back over a century and remains the first number most fans reach for to judge a pitcher. It answers a simple question: if this pitcher kept pitching at this rate, how many runs would they give up over a full nine-inning game? The calculation is earned runs divided by innings pitched, multiplied by nine to put it on a per-game scale. The crucial word is "earned." A run is unearned — and excluded from ERA — when it only scored because of a fielding error or a passed ball that the defense, not the pitcher, was responsible for. This separation is meant to credit the pitcher only for runs they genuinely allowed, though the official scorer's judgment on what counts as an error introduces some subjectivity. The other quirk that trips people up is innings notation: a third of an inning (one out) is written as .1 and two-thirds (two outs) as .2, so 180.2 innings is 180 and two-thirds, not 180.2 in decimal — a distinction this calculator handles for you.
ERA's enduring appeal is its directness: it's the actual runs that crossed the plate on a pitcher's watch, scaled to a familiar number. A starter who finishes a season around 3.00 has been excellent; the high 3.00s to low 4.00s is roughly average in a typical modern run environment; and north of 5.00 is a struggle. But the same directness is its weakness. Because ERA counts runs that scored, it absorbs everything that influenced those runs — the quality of the defense behind the pitcher, the dimensions and altitude of the ballpark, the sequencing of hits, and pure luck on balls in play. Two pitchers with identical skill can post very different ERAs based on their fielders alone. That's why analysts pair ERA with fielding-independent metrics like FIP and xFIP, which strip out defense to isolate what the pitcher actually controls.
"ERA tells you what happened; FIP tells you why. The actual runs a pitcher allowed are real — but how much of that was the pitcher, and how much the defense and luck, is a different question entirely."
Reading ERA in Context — and a Note for Global Fans
The single most important habit when using ERA is to read it against its era and environment. A 3.50 ERA in a high-offense season is more impressive than the same number in a pitcher-friendly year, which is why stats like ERA+ normalise a pitcher's ERA to the league average and adjust for ballpark (100 is average; 130 means 30% better than league). Small samples also deceive: a reliever's ERA over fifteen innings can be wrecked or flattered by a single rough outing, so treat short-sample ERAs with caution and lean on full-season or career figures. For the growing baseball audience outside the United States — including fans in Japan, Korea, Taiwan, and across Southeast Asia where the game is followed closely — the formula is identical across every professional league, from MLB to NPB to the KBO, so an ERA computed here applies anywhere the sport is played. It's the shared language of pitching, even as deeper metrics like FIP increasingly sit alongside it.
10 Facts About ERA
ERA = (earned runs ÷ innings pitched) × 9 — runs allowed per nine innings.
Only earned runs count — runs from errors or passed balls are excluded.
Innings use .1 = ⅓ and .2 = ⅔, not tenths.
A full-season starter ERA in the low 3.00s is excellent.
ERA+ normalises ERA to league average and ballpark (100 = average).
ERA absorbs defense, ballpark, and luck — not just pitcher skill.
The modern single-season record is Bob Gibson's 1.12 (1968).
Small samples swing wildly — one bad inning can wreck a reliever's ERA.
Analysts pair ERA with FIP / xFIP to separate skill from defense.
The formula is the same in MLB, NPB, KBO and every pro league.
Frequently Asked Questions
- ERA = (earned runs ÷ innings pitched) × 9. You divide the earned runs a pitcher allowed by the innings they pitched, then multiply by nine to express it as runs per nine-inning game. For example, 62 earned runs over 180 innings is (62 ÷ 180) × 9 = 3.10. Use earned runs, not total runs, and enter innings in baseball notation (the calculator converts .1 and .2 correctly).
- An earned run is one the pitcher is held responsible for. A run is unearned — and excluded from ERA — if it only scored because of a fielding error or a passed ball that extended the inning. The official scorer reconstructs the inning as if the defense had made every play, and any runs that wouldn't have scored in that clean version are unearned. Only earned runs go into ERA, so a box score lists ER separately from total runs.
- Because an inning has three outs, partial innings are counted in outs, not tenths. .1 means one out recorded (⅓ of an inning) and .2 means two outs (⅔). So 180.2 innings is 180 and two-thirds, which is 180.667 in true decimal — not 180.2. This calculator converts the notation for you, so just enter the IP exactly as it appears on the stat line. Entering 180.33 would be wrong; enter 180.1.
- For a full-season starter, an ERA in the low 3.00s is very good and the best pitchers dip into the 2.00s; the high 3.00s to low 4.00s is roughly average in a typical run environment, and above 5.00 is a struggle. But "good" depends on the era and league offense — a 3.50 in a high-scoring season beats a 3.50 in a pitcher's year. Compare to the season's league-average ERA, or use ERA+ which does that adjustment for you.
- They answer different questions. ERA records the earned runs that actually scored — a true historical result — but it's shaped by the defense, ballpark, and luck behind the pitcher. FIP isolates the outcomes a pitcher controls (strikeouts, walks, home runs) and predicts future ERA better. Use ERA to see what happened and FIP to gauge underlying skill; a large gap between them flags defense or luck. The best analysis uses both together.
- ERA+ (adjusted ERA) rescales a pitcher's ERA relative to the league average and adjusts for ballpark, with 100 set as league average. A 130 ERA+ means the pitcher was 30% better than the average pitcher that season after park adjustment; 80 means 20% worse. It lets you compare pitchers across different seasons and ballparks on a level field, which raw ERA can't do. This calculator gives raw ERA; ERA+ needs league and park data.
- Yes — you can compute a game ERA the same way (earned runs in that game ÷ innings pitched × 9), and it's how a pitcher's line is summarised. But a single game is a tiny sample: allowing 3 earned runs in 6 innings is a 4.50 game ERA, which says little about true skill. ERA is most meaningful over a full season or career; for one outing, it's just a tidy summary of that day's result.
- In the modern era, Bob Gibson posted a 1.12 ERA in 1968 — the famous "Year of the Pitcher," after which the mound was lowered to boost offense. Going back to the dead-ball era, even lower marks exist (Dutch Leonard's 0.96 in 1914), but those came in a vastly different scoring environment. For perspective, an ERA under 2.00 over a full modern season is a historic, award-winning achievement.
- No. The formula — earned runs per nine innings — is identical in MLB, Japan's NPB, Korea's KBO, Taiwan's CPBL, and every professional and amateur league worldwide. What differs is the run environment: leagues with more offense produce higher average ERAs, so to compare pitchers across leagues you'd look at how far each sits below his own league average. The raw number this calculator produces applies anywhere the game is played.
- Relievers typically post lower ERAs than starters because they pitch in short bursts at max effort, often face fewer batters per outing, and can be deployed in favourable matchups — so an "average" reliever ERA sits below an average starter's. The flip side is volatility: over a reliever's small innings total, one disastrous outing can spike the ERA dramatically, and inherited runners (a reliever who allows a previous pitcher's baserunner to score) are charged to the pitcher who put them on, not the reliever. Judge relievers over larger samples and alongside metrics like FIP and inherited-runners-stranded rate.
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