ERA Calculator - Earned Run Average

Created by Bogna Szyk and Filip Derma
Last updated: Nov 25, 2021

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 a pitcher's effectiveness 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 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 ten 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 and 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 rules change post-1920, the lowest career ERA score now belongs to Mariano Rivera (2.21), who played baseball from 1995–2013.

How to calculate ERA

The formula for calculating ERA is as follows:

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

where:

  • 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

  4. 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 the 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 1838, but it is reported to have been much earlier, in the late 1700s. In 1845, the first baseball rules came out of the Knickerbockers club, authored by Alexander Joy Cartwright, the man who would later be known as 'the father of baseball'.

Eighteen-sixty-nine saw the forming of 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 the 20th century. At 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 significant change in rules (i.e., the 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 with MLB - the National League (NL) and the American League (AL). Each of these is divided into three divisions. Thirty 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 the same, but they must meet a few specific parameters and ranges.

Baseball field diagram with infield, outfield and foul poles marked
Source: mlb.com

The infield must be a square with 90-feet sides. The area between the two foul lines formed by extending two sides of the 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 another 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 pitcher's plate should be a whitened rubber slab with dimensions of 24 inches by 6 inches. It should be 10 inches above the level of the 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 the 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 inch 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 pitcher's plate, and the 12-inch edges face the first and the third baselines. 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 build 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, which provide protection against wind, allowing them to grow straight up towards the sunlight. Forty to fifty 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 ten 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, as an amateur, will also give you many benefits. Besides all the intense emotions and fun from the competition, this activity could be an excellent way to exercise, take care of your daily calorie intake or maintain a healthy level of body fat.

Bogna Szyk and Filip Derma
Earned runs
Innings pitched
Outs pitched
ERA
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