In the sport of baseball, expressed statistically, the earned run average (ERA) is the simple average of earned runs given up by a pitcher per nine innings pitched which is also the traditional length of the game. It is computed by dividing the number of earned runs allowed by the number of innings pitched and multiplying it by nine. 

Thus, it is said that the lower the ERA, the better it is. Runs that have resulted from passed balls or defensive errors (including pitchers’ defensive errors) are recorded as unearned runs and are omitted from the ERA calculations. 

So, we can say that the ERA is calculated using the following formula:

ERA = 9 × Earned Runs Allowed / Innings Pitched

For example, a pitcher who allows 5 earned runs in 10 innings pitched would have an ERA of 4.5 (9 × 5/10).

What we are doing here is simply putting the total number of earned runs and Number of innings pitched in the calculator and then click on the compute button and you will get the result right in front of you.