ERA+ Calculator — Park & League Adjusted ERA Plus Calculator

ERA+ adjusts a pitcher's ERA for the ballpark he pitches in and the scoring environment of his league, with 100 set as exactly league average — higher is better. It is the stat analysts trust when comparing pitchers across different stadiums, teams, and eras. Enter the three inputs below and the calculator does the rest.

ERA+ Calculator

The pitcher's raw ERA
The average ERA across the league (MLB 2026: ~4.10)
100 = neutral, > 100 = hitter-friendly, < 100 = pitcher-friendly

ERA+ Formula

ERA+ = (League ERA ÷ Pitcher ERA) × (100 ÷ Park Factor) × 100

ERA+ was popularized by Baseball-Reference, and it fixes the two biggest blind spots in raw ERA. First, the league: a 3.50 ERA means something very different in a low-scoring season than in a slugfest season. Second, the park: half a pitcher's games come at home, and some home parks are launching pads while others are pitcher's paradises. ERA+ normalizes both, then rescales so that 100 is exactly average — which makes the number readable at a glance.

Worked example: a pitcher posts a 3.50 ERA in a league averaging 4.10, in a neutral park (100). Raw score: (4.10 ÷ 3.50) × 100 = 117. Park adjustment: 117 × (100 ÷ 100) = 117 ERA+ — 17% better than the league. Now move him to Coors Field (park factor 115): 117 × (100 ÷ 115) = 102 ERA+. Same arm, same ERA, but the adjustment reveals most of that shiny number was the park's doing in reverse — pitching that well at altitude is harder than it looks.

ERA+ Scale

ERA+RatingWhat It Means
200+HistoricOne of the greatest pitching seasons ever
150 – 199EliteCy Young–caliber dominance
120 – 149ExcellentAll-Star level, well above average
100 – 119Above AverageBetter than the league, reliable starter
80 – 99Below AverageBack-end or struggling arm
Below 80PoorReplacement-level performance

For a sense of the ceiling: Pedro Martínez's 2000 season posted an ERA+ of 291 — the highest single-season mark of the modern era — and Bob Gibson's 1968 campaign earned a 258. On the career side, Mariano Rivera's 205 ERA+ is the gold standard for longevity at an elite level.

Understanding Park Factor

Park factor measures how much a stadium inflates or suppresses scoring, with 100 as neutral. A factor of 108 means the park boosts scoring by roughly 8% (hitter-friendly); 94 means it suppresses scoring by about 6% (pitcher-friendly). Coors Field in Denver is the classic hitter's park, regularly posting factors of 112–118, while stadiums like Petco Park in San Diego and T-Mobile Park in Seattle have long favored pitchers.

Where do you find the inputs? League ERA is published on every major stats site — for 2026, the MLB average sits around 4.10. Park factors are published by Baseball-Reference, FanGraphs, and ESPN each season. Grab the current numbers for your pitcher's league and home park, plug them in above, and you have a genuinely context-adjusted ERA in seconds.

ERA+ — Frequently Asked Questions

  • What is ERA+? ERA+ is park- and league-adjusted ERA. It normalizes a pitcher's ERA for his home ballpark and league scoring environment. 100 is league average, and higher numbers are better — an ERA+ of 150 means 50% better than the league.
  • How is ERA+ calculated? ERA+ = (League ERA ÷ Pitcher ERA) × (100 ÷ Park Factor) × 100. First the pitcher's ERA is compared to his league, then the result is adjusted for how hitter- or pitcher-friendly his home park is.
  • What is a good ERA+? 100 is exactly league average. Anything above 100 is above average, 120+ is excellent, 150+ is elite Cy Young territory, and 200+ is a historic season.
  • Is a higher or lower ERA+ better? Higher — the opposite of raw ERA. Because ERA+ divides league ERA by pitcher ERA, better pitching produces a bigger number.
  • Who has the highest ERA+ ever? Pedro Martínez's 2000 season holds the modern single-season record at 291, followed by seasons like Bob Gibson's 258 in 1968. Mariano Rivera's 205 is the benchmark for a career.
  • What is the difference between ERA and ERA+? ERA is the raw runs-per-nine-innings number. ERA+ adjusts that number for ballpark and league scoring, making it possible to fairly compare pitchers across different stadiums, teams, and eras.
  • Where do I find league ERA and park factor? Both are published each season by Baseball-Reference, FanGraphs, and ESPN. The current MLB league-average ERA is approximately 4.10, and a neutral park factor is 100.