Baseball ERA
Calculate Earned Run Average (ERA) for baseball pitchers. Enter earned runs and innings pitched to get the official MLB stat.
Formula
ERA = 9 × Earned Runs / Innings Pitched
Multiply earned runs by 9 (length of a game), then divide by total innings pitched. Partial innings (.1, .2) count as 1/3 and 2/3 respectively.
Worked Examples
Example 1: Quality Start
Problem:3 Earned Runs in 7 Innings
Solution:(3 × 9) / 7
Result:3.86
Example 2: Complete Game Shutout
Problem:0 Earned Runs in 9 Innings
Solution:(0 × 9) / 9
Result:0.00
Example 3: Rough Outing
Problem:5 Earned Runs in 2.1 (2⅓) Innings
Solution:(5 × 9) / 2.333
Result:19.29
Frequently Asked Questions
What is ERA?
ERA stands for Earned Run Average, and it expresses how many earned runs a pitcher gives up per nine innings of work. Because it is a rate rather than a raw total, it lets you compare a starter who threw 200 innings with a reliever who threw 60. A pitcher who allows 70 earned runs in 180 innings has the same ERA as one who allows 35 in 90, even though the workloads are very different. It has been the standard headline measure of pitching effectiveness since the 1910s.
How is ERA calculated?
The formula is ERA = (Earned Runs × 9) / Innings Pitched. Multiplying by nine converts a raw run total into a per-game rate, and dividing by innings pitched removes the advantage a pitcher would otherwise get from simply throwing fewer innings. A pitcher who allowed 3 earned runs in 7 innings has an ERA of (3 × 9) / 7 = 3.86 for that outing. Season ERA uses season totals, not the average of individual game ERAs.
What is an "earned run"?
An earned run is a run the pitcher is held accountable for. To decide, the official scorer reconstructs the inning as it would have unfolded without any fielding errors or passed balls, discarding outs that should have been recorded. Runs that would not have scored in that reconstructed inning are ruled unearned and are excluded from ERA. This is why a pitcher can surrender five runs in an inning and be charged with only one: a dropped fly ball that should have been the third out makes everything after it unearned.
What is WHIP and how does it relate?
WHIP is Walks plus Hits per Inning Pitched, calculated as (Walks + Hits) / Innings Pitched. It counts baserunners allowed rather than runs scored, so it measures traffic on the bases while ERA measures the damage that traffic caused. The two usually move together, and a league-average WHIP sits near 1.30 while anything under 1.00 is elite. A pitcher with a low WHIP but a high ERA is often being hurt by home runs or by poor sequencing rather than by constant baserunners.
How do I enter partial innings?
Baseball records fractional innings in thirds because an inning is three outs. The notation 6.1 means six innings plus one out, and 6.2 means six innings plus two outs, so they convert to 6.333 and 6.667 respectively. Enter "6.1" or "6.2" directly and the calculator performs the conversion for you. Typing 6.5 instead of 6.1 is the most common mistake and will understate the ERA, because 6.5 is not a legal innings-pitched value.
Who has the lowest career ERA?
Ed Walsh holds the Major League record with a career ERA of 1.82 across 1904 to 1917, compiled in the dead-ball era when run scoring across the league was far lower than it is today. Among modern pitchers with a substantial career, Mariano Rivera is the leader at 2.21, achieved almost entirely in relief. Comparing raw ERA across eras is misleading for exactly this reason, which is why ERA+ normalises the figure to the run environment of each season.
Does ERA include runs from runners inherited?
No. When a relief pitcher enters with runners already on base and those runners score, the runs are charged to whichever pitcher put each runner on. The reliever wears only the runs from batters he himself allowed to reach. This convention protects relievers from inheriting someone else's trouble, but it also means a reliever can strand nobody and still show a clean ERA. Inherited runners scored, tracked separately, is the stat that captures that side of the job.
Why multiply by 9?
Nine is the number of innings in a standard professional game, so multiplying by nine expresses the rate as runs per complete game, which is the unit fans think in. The multiplier is not fixed by the formula itself, only by the length of the game being described. High school baseball plays seven-inning games and therefore uses 7 in place of 9, and many youth leagues that play six innings use 6, so an ERA from one level cannot be read directly against another.
Is ERA the best stat?
ERA is the most widely quoted pitching statistic, but it is not the most precise measure of skill because it credits or punishes a pitcher for the defence behind him, for the ballpark, and for the sequencing of hits. Fielding Independent Pitching strips out balls in play and grades only strikeouts, walks, hit batters and home runs. ERA+ rescales ERA to league and park, with 100 as average, so a 130 ERA+ means the pitcher was 30 percent better than league average.
Background & Theory
Earned vs. Unearned Runs:
- Earned: Runs scored via hits, walks, or home runs.
- Unearned: Runs scored due to fielding errors or passed balls.
The Math:
$$ERA = \\frac{9 \\times \\text{Earned Runs}}{\\text{Innings Pitched}}$$
Context Matters:
- League Average: Typically around 4.00 - 4.50 in modern MLB.
- Ballparks: Pitching at Coors Field (Denver, altitude) is harder than at Petco Park (San Diego, sea level). ERA+ adjusts for this.
- Role: Relievers often have lower ERAs than starters because they pitch fewer innings and can exert max effort.
Rating Scale (MLB):
- < 2.00: Historic season (Cy Young contender)
- 2.00 - 3.00: Elite / Ace
- 3.00 - 3.75: Solid #2 or #3 Starter
- 3.75 - 4.50: Back-end Starter (Average)
- > 4.50: Replacement Level / Struggling