ERA+ Calculator. Enter a pitcher's ERA, the league average ERA, and the park factor to calculate their ERA+ — an adjusted metric that accounts for ballpark effects and league context. A score of 100 is exactly league average; anything above 100 means the pitcher outperformed the league, anything below means the opposite. Great for comparing pitchers across different eras and run environments. Also try the Slugging Percentage Calculator (SLG).
ERA+ (Adjusted Earned Run Average) is a pitching statistic that normalizes a pitcher's ERA relative to the league average and the park factor of their home ballpark. A score of 100 is exactly league average. A score of 130 means the pitcher was 30% better than the average pitcher that season, after accounting for ballpark effects. See also our calculate WAR (Wins Above Replacement).
ERA+ is calculated as: ERA+ = 100 × (2 − (ERA ÷ League ERA) × (1 ÷ Park Factor)). This formula adjusts a pitcher's raw ERA for both the run-scoring environment of their home ballpark and the overall offensive level of their league.
A park factor of 1.00 means the ballpark is completely neutral — it neither favors hitters nor pitchers. Values above 1.00 (like 1.10) indicate a hitter-friendly park, while values below 1.00 (like 0.92) indicate a pitcher-friendly park. The park factor adjusts ERA+ so pitchers in hitter-friendly parks aren't unfairly penalized.
100 is the baseline (league average). An ERA+ of 120–140 is considered very good; 150+ is elite. All-time greats like Pedro Martínez and Walter Johnson posted career ERA+ values above 150. Anything below 100 means the pitcher performed worse than the league average after park adjustments.
Raw ERA doesn't account for the run-scoring environment or the ballpark a pitcher plays in. A 3.80 ERA at Coors Field (a notoriously hitter-friendly park) is far more impressive than a 3.80 ERA at Petco Park. ERA+ levels the playing field, making it possible to compare pitchers across different teams, stadiums, and even different eras of baseball.
ERA measures how many earned runs a pitcher allows per nine innings. ERA+ adjusts that number for league context and park effects, then scales it so 100 is always the average. ERA is an absolute measure; ERA+ is a relative one, making cross-era and cross-park comparisons meaningful.
Yes, ERA+ applies to any pitcher with recorded ERA data, including relievers. However, small sample sizes make ERA+ less reliable for pitchers who throw very few innings. Relievers with fewer than 20–30 innings pitched may show extreme ERA+ values that don't reflect true skill.
Baseball Reference (baseball-reference.com) is the most reliable source for both metrics. League average ERA by year is listed in their season-level stats pages. Park factors for every MLB ballpark are published annually on their team and park pages. You might also find our calculate Spin Movement Index, Active Spin (Effective RPM) & Estimated Horizontal Break — Baseball Spin Rate useful.