In baseball, earned run average (ERA) is a statistic used to measure the performance of pitchers. It is determined by dividing the number of earned runs allowed by the number of innings pitched, and multiplying by nine.

Major League Baseball recognizes the player in each league with the lowest earned run average each season. The first ERA champion in the National League was George Bradley; in the National League's inaugural 1876 season, Bradley posted a 1.23 ERA for the St. Louis Brown Stockings, allowing 78 earned runs in 573 innings pitched. The American League was established in 1901, and Hall of Fame pitcher Cy Young led that league with a 1.62 ERA for the Boston Americans during the 1901 season.

Over the course of his 17-year major league career, Lefty Grove led the American League in ERA nine times, with a career single-season low of 2.06 for the 1931 Philadelphia Athletics. Roger Clemens has won the second-most ERA titles, capturing six in the American League and one in the National League. Sandy Koufax led the National League in ERA for five consecutive seasons (1962–1966); Koufax' five awards are the most won consecutively by any player and are tied for the most awards by a player in the National League with Christy Mathewson and Clayton Kershaw. In the American League, Walter Johnson also won five ERA titles, and Pedro Martínez has won a total of five (four American League and one National League) with two different teams.

The most recent ERA champions are Cam Schlittler in the American League and Jacob Misiorowski in the National League.

The lowest single-season ERA in league history was posted by Tim Keefe, whose 0.86 ERA in 105 innings pitched for the National League's Troy Trojans in 1880 led his closest competitor by .52 runs. In the American League, Dutch Leonard's 0.96 ERA is a single-season record. Keefe and Leonard are the only two pitchers ever to allow less than one run per nine innings pitched in a single season. The widest margin of victory for an ERA champion is 1.96 runs, achieved when Martínez's 1.74 ERA led Clemens' 3.70 in the American League during the 2000 season. The largest margin of victory in the National League is 1.26 runs—Dazzy Vance's 2.61 ERA over Carl Hubbell's 3.87 in 1930. The smallest margin of victory for an ERA champion is .009 runs. Although the statistic is traditionally recorded to two decimal places by most the 1988 American League title was decided by a margin of less than one hundredth of a run when Allan Anderson's ERA of 2.446 (55 earned runs in  innings) bested Teddy Higuera's 2.455 mark (62 earned runs in  innings). Other contests decided by one hundredth or less include Luis Tiant's 1.91 ERA ahead of Gaylord Perry's 1.92 in 1972 and Mark Fidrych (2.34) over Vida Blue (2.35) in 1976.

Hoyt Wilhelm was the first pitcher in the modern era to lead both leagues in ERA (1952 with the New York Giants and 1959 with the Baltimore Orioles).

Key Year Links to the corresponding "year in baseball" or "Major League Baseball season" articleLeader Player with the lowest earned run average (ERA) in the leagueRunner-up Player with the second-best ERA in the leagueLeague Denoted only for players outside of the modern major leagues † Member of the National Baseball Hall of Fame and Museum

National League

YearLeaderERATeamRunner-upERARef 1.23 St. Louis Brown Stockings 1.56 2.11 Boston Red Caps 2.14 † 1.51 Providence Grays 1.69 1.96 Boston Red Caps 1.99 † 0.86 Troy Trojans 1.38 1.80 Detroit Wolverines † 2.13 1.95 Chicago White Stockings † 2.09 1.84 Cleveland Blues † 2.05 † 1.38 Providence Grays 1.55 † 1.58 New York Giants † 1.66 1.76 St. Louis Maroons 1.96 2.86 Philadelphia Phillies 2.90 † 1.74 New York Giants 1.90 † 2.73 Boston Beaneaters 2.96 1.95 Cincinnati Reds † 2.23 2.27 New York Giants † 2.39 † 1.93 Cleveland Spiders † 2.36 3.18 St. Louis Browns † 3.23 † 2.78 New York Giants 3.70 2.45 Washington Senators 3.18 2.45 Cincinnati Reds † 2.83 † 2.54 New York Giants † 2.64 † 1.88 Chicago Orphans 2.10 † 2.50 Boston Beaneaters † 2.58 † 2.37 Pittsburgh Pirates 2.41 2.18 Pittsburgh Pirates 2.22 1.33 Chicago Orphans 1.77 2.06 Pittsburgh Pirates † 2.26 † 1.61 New York Giants 1.68 † 1.28 New York Giants 1.42 † 1.04 Chicago Cubs 1.51 1.15 Chicago Cubs 1.17 † 1.43 New York Giants † 1.47 † 1.14 New York Giants † 1.31 1.80 Chicago Cubs † 1.86 † 1.99 New York Giants 2.31 1.96 New York Giants † 2.12 † 2.06 New York Giants 2.15 1.72 St. Louis Cardinals 1.90 † 1.22 Philadelphia Phillies 1.58 † 1.55 Philadelphia Phillies † 1.58 1.44 New York Giants † 1.83 1.74 Chicago Cubs 2.00 † 1.72 Chicago Cubs 1.79 † 1.91 Chicago Cubs 2.16 2.59 St. Louis Cardinals 2.64 2.63 New York Giants 3.01 1.93 Cincinnati Reds † 2.80 † 2.16 Brooklyn Robins 2.69 2.63 Cincinnati Reds † 2.88 2.61 Pittsburgh Pirates 2.82 2.47 Pittsburgh Pirates † 2.52 † 2.09 Brooklyn Robins 2.47 3.09 New York Giants † 3.13 † 2.61 Brooklyn Robins † 3.87 2.26 New York Giants † 2.65 2.37 Chicago Cubs † 2.50 † 1.66 New York Giants 2.00 † 2.30 New York Giants † 2.66 2.58 Pittsburgh Pirates 2.70 † 2.31 New York Giants 2.87 2.38 Boston Bees 2.61 2.66 Chicago Cubs 2.86 2.29 Cincinnati Reds 2.60 2.48 Cincinnati Reds 2.50 2.24 Cincinnati Reds 2.34 1.78 St. Louis Cardinals 2.13 1.90 St. Louis Cardinals 2.30 2.38 Cincinnati Reds 2.40 2.40 Chicago Cubs 2.46 2.10 St. Louis Cardinals 2.21 † 2.33 Boston Braves 2.47 2.24 St. Louis Cardinals 2.51 2.50 New York Giants 2.73 2.71 New York Giants 2.97 2.88 Boston Braves 2.93 † 2.43 New York Giants 2.58 † 2.10 Milwaukee Braves † 2.75 2.30 New York Giants 2.76 2.83 Pittsburgh Pirates 3.20 2.70 Milwaukee Braves † 2.78 2.66 Brooklyn Dodgers † 2.69 2.47 San Francisco Giants 2.88 2.83 San Francisco Giants 2.84 2.70 San Francisco Giants 2.74 † 3.02 Milwaukee Braves 3.10 † 2.54 Los Angeles Dodgers 2.80 † 1.88 Los Angeles Dodgers 2.11 † 1.74 Los Angeles Dodgers † 2.18 † 2.04 Los Angeles Dodgers † 2.13 † 1.73 Los Angeles Dodgers 2.22 † 1.87 Atlanta Braves † 2.29 † 1.12 St. Louis Cardinals 1.99 † 2.10 San Francisco Giants † 2.17 † 2.82 New York Mets 3.02 † 1.76 New York Mets 2.10 † 1.97 Philadelphia Phillies 1.99 † 2.08 New York Mets † 2.42 2.28 Atlanta Braves † 2.38 2.24 San Diego Padres 2.29 2.52 St. Louis Cardinals 2.57 2.34 Pittsburgh Pirates † 2.58 2.43 New York Mets 2.47 2.71 Houston Astros 2.76 † 2.20 Los Angeles Dodgers † 2.34 † 1.69 Houston Astros 2.18 2.40 Montreal Expos 2.47 2.25 San Francisco Giants 2.37 2.48 Los Angeles Dodgers 2.60 1.53 New York Mets 1.93 2.22 Houston Astros 2.57 † 2.76 Houston Astros 3.03 2.18 St. Louis Cardinals 2.22 2.28 San Francisco Giants 2.31 2.21 Houston Astros 2.55 2.39 Montreal Expos 2.51 2.08 San Francisco Giants 2.16 † 2.36 Atlanta Braves 2.48 † 1.56 Atlanta Braves 2.74 † 1.63 Atlanta Braves 2.54 1.89 Florida Marlins † 2.72 † 1.90 Montreal Expos † 2.20 † 2.22 Atlanta Braves 2.38 † 2.48 Arizona Diamondbacks 2.68 2.58 Los Angeles Dodgers † 2.64 † 2.49 Arizona Diamondbacks 2.98 † 2.32 Arizona Diamondbacks † 2.62 2.34 San Francisco Giants 2.39 2.27 San Diego Padres † 2.60 1.87 Houston Astros 2.39 2.98 Houston Astros 3.09 2.54 San Diego Padres 3.01 2.53 New York Mets 2.62 2.24 St. Louis Cardinals 2.48 2.30 Florida Marlins 2.42 2.28 Los Angeles Dodgers † 2.35 2.53 Los Angeles Dodgers 2.73 1.83 Los Angeles Dodgers 2.19 1.77 Los Angeles Dodgers 2.25 1.66 Los Angeles Dodgers 1.77 2.13 Chicago Cubs 2.44 2.31 Los Angeles Dodgers 2.51 1.70 New York Mets 2.37 2.32 Los Angeles Dodgers 2.43 1.73 Cincinnati Reds 2.01 2.43 Milwaukee Brewers 2.46 2.16 Los Angeles Dodgers 2.28 2.25 San Diego Padres 2.98 2.38 Atlanta Braves 2.57 1.97 Pittsburgh Pirates 2.49 1.80 Milwaukee Brewers 2.16

Notes While Baseball-Reference.com lists both Niekro and Joaquín Andújar with an ERA of 2.47 in 1982, Niekro's average is lower (2.467) than Andújar's (2.473) if extended to three decimal places.

American League

YearLeaderERATeamRunner-upERARef † 1.62 Boston Americans 2.42 1.91 Detroit Tigers † 2.05 1.74 Cleveland Naps † 2.08 † 1.59 Cleveland Naps † 1.62 † 1.48 Philadelphia Athletics 1.76 1.52 Chicago White Sox 1.59 † 1.60 Chicago White Sox 1.78 † 1.16 Cleveland Naps † 1.26 1.39 Philadelphia Athletics † 1.41 † 1.27 Chicago White Sox 1.30 1.80 Cleveland Naps † 1.90 † 1.39 Washington Senators 1.91 † 1.14 Washington Senators 1.58 0.96 Boston Red Sox 1.70 1.49 Boston Red Sox † 1.55 † 1.75 Boston Red Sox 1.78 1.53 Chicago White Sox 1.74 † 1.27 Washington Senators † 1.82 † 1.49 Washington Senators 1.82 2.45 New York Yankees † 2.49 † 2.48 Chicago White Sox 3.00 † 2.81 Chicago White Sox 2.85 † 2.76 Washington Senators † 3.02 † 2.72 Washington Senators 2.75 † 2.84 Washington Senators † 2.96 † 2.51 Philadelphia Athletics 2.83 2.28 New York Yankees † 2.63 2.51 Washington Senators † 2.56 † 2.81 Philadelphia Athletics 3.06 † 2.54 Philadelphia Athletics 3.31 † 2.06 Philadelphia Athletics † 2.67 † 2.84 Philadelphia Athletics † 3.09 2.95 Cleveland Indians 3.09 † 2.33 New York Yankees 2.61 † 2.70 Boston Red Sox † 3.02 † 2.81 Boston Red Sox 3.44 † 2.33 New York Yankees 2.40 † 3.08 Boston Red Sox † 3.31 † 2.54 Boston Red Sox † 2.76 † 2.61 Cleveland Indians 2.83 2.37 Chicago White Sox 2.97 † 2.10 Chicago White Sox 2.27 1.64 New York Yankees 2.27 2.12 Detroit Tigers † 2.22 † 1.81 Detroit Tigers 2.02 † 1.94 Detroit Tigers 2.10 2.42 Chicago White Sox † 2.68 2.43 Cleveland Indians 2.82 2.36 Cleveland Indians 2.77 † 3.20 Cleveland Indians 3.39 2.78 Chicago White SoxDetroit Tigers 2.91 2.06 New York Yankees 2.37 2.42 New York Yankees 2.72 2.64 Cleveland Indians 2.69 1.97 Chicago White Sox † 2.63 † 2.47 New York Yankees 2.53 2.45 New York Yankees 2.54 † 2.01 New York Yankees 2.68 † 2.19 Baltimore Orioles 2.64 2.67 Chicago White Sox † 2.79 2.40 Washington Senators 2.68 2.21 Detroit Tigers † 2.78 2.33 Chicago White Sox 2.39 1.65 Los Angeles Angels 1.88 2.18 Cleveland Indians 2.40 1.98 Chicago White Sox 2.43 2.06 Chicago White Sox 2.28 1.60 Cleveland Indians 1.81 2.19 Washington Senators † 2.34 2.56 Oakland Athletics † 2.71 1.82 Oakland Athletics 1.91 1.91 Boston Red Sox † 1.92 † 2.40 Baltimore Orioles † 2.52 † 2.49 Oakland Athletics † 2.51 † 2.09 Baltimore Orioles † 2.58 2.34 Detroit Tigers 2.35 2.54 California Angels † 2.72 1.74 New York Yankees 2.27 2.78 New York Yankees 2.96 2.46 New York Yankees 2.53 2.32 Baltimore Orioles 2.33 2.96 Cleveland Indians 3.10 2.42 Texas Rangers 2.77 2.79 Baltimore Orioles 2.83 2.48 Toronto Blue Jays 2.69 2.48 Boston Red Sox 2.79 2.76 Toronto Blue Jays 2.90 2.45 Minnesota Twins 2.45 2.16 Kansas City Royals 2.57 1.93 Boston Red Sox 2.40 2.62 Boston Red Sox 2.65 2.41 Boston Red Sox 2.46 2.56 Kansas City Royals 2.95 2.65 Oakland Athletics 2.85 † 2.48 Seattle Mariners 2.95 2.93 Toronto Blue Jays 3.22 2.05 Toronto Blue Jays † 2.28 2.65 Toronto Blue Jays † 2.89 † 2.07 Boston Red Sox 3.44 † 1.74 Boston Red Sox 3.70 3.05 Seattle Mariners † 3.15 † 2.26 Boston Red Sox 2.58 † 2.22 Boston Red Sox 2.70 2.61 Minnesota Twins 3.26 2.86 Cleveland Indians 2.87 2.77 Minnesota Twins † 3.19 3.01 Los Angeles Angels of Anaheim 3.06 2.54 Cleveland Indians † 2.78 2.16 Kansas City Royals 2.49 2.27 Seattle Mariners 2.33 2.40 Detroit Tigers 2.41 2.56 Tampa Bay Rays 2.64 2.57 Detroit Tigers 2.65 2.14 Seattle Mariners 2.17 2.45 Detroit TigersToronto Blue Jays 2.48 3.00 Toronto Blue Jays 3.04 2.25 Cleveland Indians 2.90 1.89 Tampa Bay Rays 2.21 2.50 Houston Astros 2.58 1.63 Cleveland Indians 1.99 2.84 Toronto Blue Jays 3.16 1.75 Houston Astros 2.20 2.63 New York Yankees 2.79 2.39 Detroit Tigers 2.80 2.21 Detroit Tigers 2.43 1.95 New York Yankees 2.40

Notes While Baseball-Reference.com lists both Scarborough and Hall of Famer Bob Lemon with an ERA of 2.82 in 1948, Scarborough's average is lower (2.817) than Lemon's (2.820) if extended to three decimal places. While Baseball-Reference lists both Anderson and Higuera with an ERA of 2.45 in 1988, Anderson's average is lower (2.446) than Higuera's (2.455) if extended to three decimal places.