What this calculator does
ERA is earned runs multiplied by nine and divided by innings pitched: how many earned runs a pitcher would concede over a full nine-inning game at their current rate. Thirty-eight earned runs over 180 innings gives an ERA of 1.90.
The nine is what makes it interpretable. Without it the figure would be runs per inning, which is a small decimal that means little at a glance. Scaling to a game length turns it into a number that can be compared directly against a scoreline.
The formula
Earned runs are multiplied by nine and divided by innings pitched. Innings should be entered as decimal thirds: 6.33 for six and one third rather than the baseball notation 6.1, which the calculator would read as six and one tenth. Only earned runs count, so runs scoring because of errors are excluded.
| Term | Meaning |
|---|---|
| Earned run | A run that scored without the aid of an error or passed ball. |
| Unearned run | A run attributed to a defensive mistake, which does not count against the pitcher ERA. |
| Nine innings | The scaling factor, making ERA a per-game figure. |
| FIP | Fielding independent pitching, an alternative built only from strikeouts, walks and home runs. |
The inputs explained
| Field | What to enter |
|---|---|
| Earned runs allowed | Earned runs allowed. Unearned runs are excluded. |
| Innings pitched | Innings pitched, as decimal thirds. Enter 180.33 rather than 180.1 for 180 and one third. |
When to use it
Evaluating a pitcher season
ERA remains the headline pitching statistic and the one most widely quoted despite its known limitations.
Comparing starters and relievers
ERA normalises for innings pitched, which is what allows a reliever throwing 70 innings to be compared against a starter throwing 200.
Tracking a run of form
Calculating ERA over a recent stretch rather than the full season shows current form, which the season figure smooths away.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
What ERA does each earned run total give?
A fixed innings total against a range of earned runs allowed.
Questions
What is a good ERA?
Under 3.00 is very good, around 4.00 is league average in the modern game and above 5.00 is poor. The bands move substantially between eras: a 3.50 ERA meant something quite different in 1968 than in 2000, which is why era-adjusted versions such as ERA+ exist.
What is the difference between earned and unearned runs?
An unearned run scored because of a defensive error or passed ball and would not have scored otherwise. It does not count against the pitcher. The distinction is a scorer judgement, which is one of the criticisms of the statistic.
How do I enter innings pitched?
As decimal thirds. Baseball writes 6.1 for six and one third innings, which is not a decimal. Enter 6.33 instead. Entering 6.1 would be read as six and one tenth and give a slightly wrong ERA.
Why is ERA criticised?
Because it depends heavily on defence, on sequencing and on the scorer earned-run judgement, none of which the pitcher controls. FIP and similar measures were developed to isolate what the pitcher does control, and they often disagree with ERA over a single season.
For baserunners allowed, see the WHIP calculator. For hockey goals against, see the GAA calculator.