What Is ERA In Baseball?

Because he’s the player who spends most of his time right in the thick of the action, the performance of a baseball team’s pitcher is nearly always subject to deeper scrutiny than that of any of his fellow players.

It follows that the accuracy and speed at which a pitcher throws the ball at an opposing team’s batters makes a big difference to how his team performs. His ability to consistently maintain a high level of both these characteristics when under lots of pressure marks him out as playing a key role in any successful baseball team.

The number runs he concedes is a broad statistic by which a pitcher’s effectiveness can be judged – but because he can also concede runs which are not directly attributable to how well he pitches the ball, the pitcher’s Earned Run Average, or ERA, was devised as a more effective way of evaluating his contribution to his team’s fortunes.

What Is ERA In Baseball?

A pitcher has a pretty simple job in the game of baseball – to throw the ball in a certain way for the batters in the opposing team. But he is constantly trying to stop his opponents from hitting the kind of powerful shots which help them get around the bases and, ultimately, score home runs

So his Earned Run Average, or ERA, reflects how good he is at achieving this objective. It is a calculation of the number of earned runs that he allows on average per nine innings, or completed game, pitched. This is done by taking the total number of earned runs the pitcher has conceded, and dividing it by the number of innings pitched, then multiplying it by nine.

The lower the pitcher’s ERA, that is, the fewer average runs he concedes over all of the nine-inning games in which he participates, the more likely it is that his pitching will contribute to his team winning the majority of its games.

So the formula for calculating a pitcher’s ERA can be expressed mathematically as:


[(Number of earned runs conceded) x 9/(Number of innings pitched)]


It’s important to recognise, though, that a pitcher’s ERA doesn’t tell the entire story, as different sets of circumstances can lead to wild swings in what is considered a ‘normal’ ERA and likewise what is considered good or bad. 

So as part of this article delving into one of the more intricate rules of baseball, we will set out what contributes to a good ERA, but before that, we also need to consider the difference between earned runs and unearned runs.

What Is The Difference Between Earned and Unearned Runs in Baseball?

Earned runs are those achieved by the skill of a batter, where he successfully anticipates the action of the pitcher facing him, and so gets himself in the best position and times his stroke to be able to hit the ball far enough and sufficiently far from the reach of the opposing team’s fielders to allow him to advance to one of the bases, or even to score a home run. So it can in no way be attributed to any fault in the action of the pitcher.

By contrast, unearned runs, while still being accumulated in the same way, of the batting team’s players running between the bases, come from what’s considered to be a bad pitch.

So each time he throws the ball, the pitcher is trying to minimize the chances of the batter hitting the ball, either through his pitching skill, or by not pitching in a way which gives the batter a better chance of a clean strike. 

The pitcher’s ERA is also a reflection of how well his team-mates perform behind the bat, in catching the ball when the batter fails to hit it.

Earned runs make up the vast majority of all those scored in baseball – during the 2019 season, they accounted for 92 per cent of all the runs accumulated.
An average of three unearned runs were scored for every four games over the same period, or 0.75 unearned runs per game – so you could quite easily have a whole game in which no unearned runs are scored, meaning that the pitchers can be said to have done a good day’s work. 

However, the degree to which a pitcher actually contributes to the batting team’s scoring through his wayward throwing is still matter of regular debate among baseball aficionados, because while some errors clearly allow the base runners to make some ground between bases, it is often arguable whether an error was bad enough to actually allow him to reach base.

What Constitutes A Good ERA in Baseball?

Rating Earned Run Average (ERA)
Exceptional 2.00 and under
Excellent 2.00–3.00
Above Average 3.00–4.00
Average 4.00–5.00
Below Average 5.00–6.00
Poor 6.00 and above


When Was ERA First Used As A Statistic In Baseball?

The idea of ranking pitchers by their ERAs came about relatively early in baseball’s history, as it was soon realized that the standard measure of games won and lost didn’t fully reflect their contribution to the overall scorelines.

One of the sport’s first specialist writers and statisticians, by the name of Henry Chadwick, realized that it needed more than the simple figures of games won and lost to properly evaluate a pitcher’s contribution to his team.

However, it took many decades for Chadwick’s work to more fairly apportion runs to the quality of a pitcher’s throws to be officially recognized, and it wasn’t until 1912 that the ERA was added to official game statistics by the NBA.

While ERA has its shortcomings, it has come to be recognized as a useful statistic for pitting pitchers against each other, and giving an indication of their overall value to their team’s performance.