What is ERA in Baseball?

Last updated on October 31st, 2023 at 01:36 pm

An earned run allowed (ERA) is any run scored as the direct result of a pitch rather than a fielding error or another factor. Conversely, an unearned run occurs during a mistake by another play, like a throwing error.

A pitcher’s main objective is to prevent the other team’s hitters from earning runs. A pitcher’s ERA represents the average number of runs they allow in a nine-inning game, so it is a pretty important measure for how well they achieve their objective.

So, at its most basic, an ERA is a pitching statistic that calculates how many earned runs a pitcher allows for every nine innings pitched. It gives a pretty accurate “ballpark figure,” so to speak, for how well a pitcher is performing throughout the season.

Table of Contents

What is the Formula to Calculate ERA?

ERA calculation is pretty simple. The formula for calculating ERA is:
(total number of earned runs allowed ÷ total number of innings pitched) x 9

This number gives you the average number of earned runs allowed per inning. ERAs are two decimal places and averages over a season or a career for a pitcher, depending on what you want to review.

So, for example, let’s look at a pitcher who has pitched 100 innings in a season. In those 100 innings, they’ve allowed 50 total runs. Of those 50 runs, only 40 of the runs were earned, and 10 were unearned runs. To calculate this pitcher’s ERA, you would divide 40 by 100 and then multiply by 9. This ERA comes out to a 3.60 for that pitcher.

What Happens if a Pitcher Leaves the Game with Men on Base and they Score?

It is important to note that if a pitcher exits a game with runners on base, any runs earned by those runners still count against their ERA since they pitched to those runners and allowed them to get on base.

Is a High or Low ERA Better in Baseball?

A pitcher’s main objective is to prevent the other team’s hitters from earning runs. A lower ERA means that the pitcher has allowed fewer earned runs. Therefore, a low ERA is a better score than a high ERA.

In 21st century baseball, an ERA below 4.00 is considered good, and anything below 3.00 is great. An ERA below 2.00 is rare and signifies an exceptional pitcher. Anything above 5.00 is terrible, and generally, pitchers with that ERA either pitch during blow-out games or get sent to the minor leagues.

How is ERA Different for a Starter vs. a Reliever?

The primary difference between a starter and a reliever is how many innings they pitch during a game. For example, a starter might only throw six innings one day a week. That means the pitcher needs to pace themselves to last six innings, so they might not throw as hard or pitch to contact to get batters out quickly.

On the other hand, a reliever might pitch six innings in a week, but they do that over six games. That means a reliever only has to pitch one inning during a baseball game, which means they can throw harder against hitters since it’s more of a sprint than a marathon in pitcher terms. However, a reliever who comes in during one inning might give up many runs, which would make their ERA look out of whack for that game compared to a starting pitcher.

Can You Have a Zero ERA in Baseball?

You might be surprised to learn that earned runs account for over 90% of runs in baseball. Unearned runs are relatively rare. This earned run metric results in ERA scores being higher than you might initially think.

Players can have a zero ERA listed, but this is not usually accurately representing their skill. Zero ERAs are also sometimes called undefined or infinite ERAs.

Zero ERAs are usually reported at the beginning of a season before there are statistics to report on complete games. If a pitcher allows one or more earned runs without retiring a batter, they will technically have a zero ERA since they did not record any outs. However, a pitcher has never sustained an ERA of zero for an entire season.

Conclusion: What is ERA in Baseball?

In summary, ERA is a great way to evaluate a pitcher’s effectiveness in limiting how many earn runs they give up over nine innings. For example, the ERA stat line is a better metric instead of how many wins a pitcher got. However, if you look for the best stat line for pitchers, baseball WHIP might be the best metric since that measures how many walks and hits they give up per inning.