ERA Calculator (Earned Run Average)

By Bogna Szyk and Filip Derma
Last updated: Jun 03, 2020

If you're a baseball fan, this ERA calculator is right in your ballpark. It finds the value of the Earned Run Average - a metric that measures the effectiveness of a pitcher in a much more accurate way than a simple win-to-lose ratio. Read on to learn the principles of this statistic - what is ERA in baseball, and how to calculate the ERA of an arbitrary player. Moreover, in the article below you can find a brief summary of baseball history, a description of the most iconic baseball organization - Major League Baseball, and some technical information about a baseball field and a baseball bat. Finally, you'll have a chance to take a look at the MLB ERA leaders of the last 10 years.

What is ERA in baseball?

To put it simply, ERA is a measure of a pitcher's effectiveness. It takes his performance over all nine innings but also takes into account the time he has been pitching.

By definition, it is the mean of earned runs given up by a pitcher per the total of innings pitched (9 for a regular game, 7 for softball, and 6 or 7 for little league games). If any defensive errors occur during the game, the run is considered unearned and is not taken into account for ERA calculations.

Generally, the lower the ERA score, the better. The lowest career earned run average in history is 1.82, held by Ed Walsh, who played from 1904 to 1917. After the change of rules post-1920, the lowest career ERA score now belongs to Mariano Rivera (2.21), who played baseball in years 1995–2013.

How to calculate ERA?

The formula for calculating ERA is as follows:

ERA = (earned runs / innings pitched) * game innings


  • Earned runs is the number of runs scored while the pitcher was on the mound. As mentioned before, a defensive error leads to an unearned run.
  • Innings pitched is each full inning (3 outs) that the pitcher has been on the mound. For partial innings, each out pitched counts as 1/3 of an inning.
  • Game innings: typically, this value is equal to 9. It can be lower for softball games or little league games. You can change this parameter in the advanced mode.

For example, let's assume that a pitcher has pitched 65 innings and 2 outs and has allowed 15 earned runs. In such a case, you can calculate his ERA score as follows:

  1. Calculate the number of innings pitched, considering each out as a third of a full inning. In this case, innings pitched = 65 + 2/3 = 65.67.
  2. Write down the number of innings per game. Let's assume game innings = 9.
  3. Input these values to the ERA formula:

ERA = (earned runs / innings pitched) * game innings

ERA = (15 / 65.67) * 9

ERA = 2.06

  1. The ERA score of this pitcher is equal to 2.06.

Baseball history

Baseball has its own unique and incontestable place in the hearts of American people - more than any other sport. Over the course of a baseball game you can feel a wide array of emotions like wonder, euphoria, and pride (and sadness if your team loses). These are all very common for any baseball fan. This game has a democratic character; it can be played by any person of an average height and weight (unlike basketball, for example). Thanks to all these characteristics, it has become the national pastime of the United States of America.

It is believed that baseball has its roots in the British game of rounders. It is also closely related to cricket, because both games have two teams alternating between offense and defense and they center around throwing a ball, using a 'bat' and running into a 'base'. The first documented baseball game was in the year 1838, but it is reported much earlier, in the late 1700s. In 1845, first baseball rules come out of the Knickerbockers club; authored by Alexander Joy Cartwright, the man who would later be known as 'the father of baseball'.

1869 saw the forming the first professional team - the Cincinnati Red Stockings. Thanks to them, by the end of the century baseball had become the national pastime in the US. A few years later, the first modern World Series was founded, and then the major leagues were formed: in 1876 the National League, and in 1903 the American League.

Baseball had its golden years in the early years of 20th century. In that time, many large stadiums were built for larger clubs (e.g., Fenway Park in Boston or Ebbets Field in Brooklyn). The year 1920 brought a new baseball era with a major change in rules (i.a. introduction of the power hitter).

Major League Baseball

Major League Baseball (commonly known as MLB) is the name of the professional baseball organization, and is one of the four oldest, major and professional sports leagues in the U.S. and Canada. There are two leagues (already mentioned above) associated within MLB - the National League (NL) and the American League (AL). Each of these is divided into three divisions. 30 teams play in Major League Baseball, 15 in each league (NL and AL).

The word 'major' in the organization name means that it is the highest league in which you can play professional baseball. Currently, only two leagues, National and American, have the status of 'major league', but, in theory, it is possible to create another major league. This is unlikely to happen though; it would be problematic to find enough new clubs on the same organizational and (especially) financial level as the clubs from the NL and AL.

The last attempt to create a third league in MLB was in the 1950s, but the creation of the Continental League failed. Professional leagues which are not affiliated with MLB are members of Minor League Baseball.

Baseball field

Because of its characteristic shape (quite extraordinary, unlike e.g. football or rugby pitches) baseball fields are also known as 'baseball diamonds'. Across the Major League, not all ballparks are exactly the same, but there are a few specific parameters and ranges that must be met.

Baseball field diagram with infield, outfield and foul poles marked


The infield must be a square, with 90-feet sides. The area between the two foul lines formed by extending two sides of said square is called the outfield. The field must be constructed to have all the bases at the same height as the home plate. The minimum distance between home plate and the nearest fence, stand or other obstruction on the left/right field foul lines is 325 feet. The distance from the home plate to the nearest fence, stand or other obstruction in the center field should be at least 400 feet.

The pitchers plate should be a whitened rubber slab with dimensions of 24 inches by 6 inches. It should be 10 inches above the level of home plate and be 6 inches away from the back point of the home plate. It is placed 18 inches behind the center of the mound. The mound is within a circle with an 18-foot diameter, and is also surrounded by a level area that is 5 feet by 34 inches. The slope of pitcher's mound decreases 1 inch per every foot (for 6 feet in the direction of home plate), starting from 6 inches in front of the pitcher's plate.

The home plate is a 17 inches square covered with whitened rubber. Two of its corners are removed, so that one edge is 17 inches, the pair of adjacent sides are 8.5 inches each, and the remaining two are 12 inches each, set with an angle to create a point. The 17 inch edge faces the pitchers plate, and the 12 inch edges face the first and the third base lines. The back tip of the home plate must be 127 feet, 3 and 3/8 inches away from second base.

The remaining bases are filled with soft material and must be 15 inch squares, with the thickness ranging from 3 to 5 inches. White canvas (or rubber) covers the bases.

Baseball bat

The baseball rules provide some limitations regarding bats for professional play. Modern bats should be at least 42 inches (107 cm) long, with a diameter up to 2.75 inches (7 cm). There are no restrictions on weight. The bat should be made of wood, without any kind of reinforcement (e.g., steel) inserted into its center.

The same raw materials have been used to building the baseball bats for years. Traditionally, ash trees originating from Pennsylvania and New York state are considered the best material for bats. Ash wood is lightweight, strong, and flexible, valuable traits in a raw material. The best trees grow in dense clusters, what provides protection against wind and allows them to grow straight up towards the sunlight. 40-50 years of tree growth is required to bring an ash tree to the preferred 14-16 inches (36-41 cm) trunk diameter. Making about 60 bats from each ash tree is then perfectly possible.

MLB ERA leaders

As mentioned above, there are two players with the best career ERA-score in history: Ed Walsh (1.82) and, after the change in rules, Mariano Rivera (2.21). Major League Baseball seasonally recognizes players with the lowest earned run average (separately in each league). Let's take a look at the best seasonal ERA players for the last 10 years.

  • National League
Year Leader ERA Team
2018 Jacob deGrom 1.70 New York Mets
2017 Clayton Kershaw 2.31 Los Angeles Dodgers
2016 Kyle Hendricks 2.13 Chicago Cubs
2015 Zack Greinke 1.66 Los Angeles Dodgers
2014 Clayton Kershaw 1.77 Los Angeles Dodgers
2013 Clayton Kershaw 1.83 Los Angeles Dodgers
2012 Clayton Kershaw 2.53 Los Angeles Dodgers
2011 Clayton Kershaw 2.28 Los Angeles Dodgers
2010 Josh Johnson 2.30 Florida Marlins
2009 Chris Carpenter 2.24 St. Louis Cardinals
2008 Johan Santana 2.53 New York Mets
  • American League
Year Leader ERA Team
2018 Blake Snell 1.89 Tampa Bay Rays
2017 Corey Kluber 2.25 Cleveland Indians
2016 Aaron Sanchez 3.00 Toronto Blue Jays
2015 David Price 2.45 Detroit Tigers Toronto Blue Jays
2014 Félix Hernández 2.14 Seattle Mariners
2013 Aníbal Sánchez 2.57 Los Angeles Dodgers
2012 David Price 2.56 Tampa Bay Rays
2011 Justin Verlander 2.40 Detroit Tigers
2010 Félix Hernández 2.27 Seattle Mariners
2009 Zack Greinke 2.16 Kansas City Royals
2008 Cliff Lee 2.54 Cleveland Indians

Let's play baseball!

As you can see, baseball is a unique sport that touches millions of hearts and somehow has become an integral part of American identity. Baseball players are well-known national celebrities and professional sportsmen. They need to train regularly, exercise a lot, keep an ideal weight and diet (strictly prescribed amount of proteins, carbohydrates etc.) to be fit for the whole season. That is how the life of a professional sportsman looks like. However, playing baseball on your own, as an amateur, will also give you many benefits. Besides all the strong emotions and fun from competition, this activity could be a good way to exercise, take care of your daily calorie intake or maintain a healthy level of body fat.

Bogna Szyk and Filip Derma
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