ERA Calculator - Earned Average Run

What the ERA calculator does

ERA, short for earned run average, is the headline number on a pitcher's line, the one most people glance at first. This tool works it out. You give it the earned runs a pitcher has allowed and the innings they have pitched, and it returns their ERA, the earned runs they give up per nine innings, which is to say per full game's worth of work.

It is the closest thing pitching has to a bottom line. There are two small things worth understanding to read it right, the innings figure and the word earned, and both are covered below.

How to use it

1. Enter the earned runs. Runs that scored without the help of a defensive error, which is the distinction explained further down.
2. Enter the innings pitched. Be careful with the decimal here, because baseball counts partial innings in thirds, not tenths, which is the very next section.

Press Calculate ERA for the result, or Reset to clear the boxes.

How ERA is worked out

You take the earned runs per inning and scale them up to a full nine-inning game:

ERA = (earned runs × 9) ÷ innings pitched

The times-nine is the key. A pitcher rarely throws exactly nine innings, so ERA puts everyone on the same footing by asking, at this rate, how many earned runs would this pitcher give up over a complete game. That is why a reliever who threw 40 innings and a starter who threw 200 can be compared directly: both numbers are expressed per nine.

A note on innings pitched

Here is the catch that quietly trips people up. In baseball, innings pitched are recorded in thirds, because an inning is three outs. So a line of 6.1 innings means 6 innings and 1 out, which is 6 and a third. And 6.2 innings means 6 innings and 2 outs, which is 6 and two-thirds. It does not mean 6.1 or 6.2 as a plain decimal.

That matters here, because this calculator does the division on the number you type. So before you enter a figure with a partial inning, convert the outs to a real fraction: 1 out is a third, which is 0.33, and 2 outs is two-thirds, which is 0.67. A pitcher who threw 6 and 2 thirds should be entered as 6.67, not 6.2. Do that and your ERA will be exactly right.

What "earned" actually means

This is the heart of the stat, and it is genuinely fair-minded. ERA only counts earned runs, the runs a pitcher gives up through their own work, hits, walks, and the like. It leaves out unearned runs, the ones that only scored because the defense behind the pitcher made a mistake. If a fielder boots a routine grounder and a run scores that should not have, that run is unearned, and it does not go on the pitcher's ERA.

The thinking is simple and decent: a pitcher should be judged on what they can control, not punished for an error someone else made. So when you enter earned runs, you are entering only the runs that were genuinely the pitcher's responsibility. Unearned runs still hurt the team on the scoreboard, they just do not stain the pitcher's average.

An example with real numbers

Say a starter has allowed 70 earned runs across 200 innings on the season.

• ERA = (70 × 9) ÷ 200 = 630 ÷ 200 = 3.15

So this pitcher is giving up 3.15 earned runs per nine innings, which is a very good season. Read it as: if they pitched a full nine-inning game at their season rate, you would expect a little over three earned runs against them.

What a good ERA looks like

Lower is always better, since it is runs allowed. As a rough guide at the major league level, an ERA under 3.00 is elite, the kind of number that gets a starter into the award conversation. Roughly 3.00 to 4.00 is good, 4.00 to 5.00 is around league average, and above 5.00 is a problem. Two caveats keep you honest, though. ERA shifts with the era and the ballpark, a hitter-friendly park inflates it, and because it leans on the defense behind the pitcher, it is best read alongside a stat like WHIP, which counts baserunners directly and often hints at where an ERA is heading next.

Questions people ask

How do you calculate ERA?

Multiply earned runs by nine, then divide by innings pitched. A pitcher with 70 earned runs in 200 innings has an ERA of 3.15.

How do I enter innings like 6.2?

Convert the outs to thirds first. The 2 in 6.2 means 2 outs, which is two-thirds, so enter 6.67. Innings are counted in thirds, not tenths, so a plain 6.2 would give a slightly wrong ERA.

What is the difference between earned and unearned runs?

Earned runs are the pitcher's own responsibility, scored through hits, walks, and the like. Unearned runs only scored because of a defensive error, and they do not count against ERA, since the pitcher did not cause them.

What is a good ERA?

At the major league level, under 3.00 is elite, 3.00 to 4.00 is good, 4.00 to 5.00 is about average, and above 5.00 is poor. The number is lower-is-better and shifts with the ballpark and era.

References

1. MLB.com Glossary, Standard Stats: Earned Run Average (ERA). https://www.mlb.com/glossary/standard-stats/earned-run-average