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ERA Calculator

Work out a pitcher's earned run average from earned runs and innings pitched, reading 6.1 and 6.2 as thirds of an inning.

Level: Grades 6–7

Printable worksheet

ERA Calculator

Know the answer you need? Pick an input to work backward.

Inputs

In baseball notation, 180.2 means 180⅔ innings.

Each out is a third of an inning, so box scores write the extra outs after the point: 6.1 is 6⅓ innings and 6.2 is 6⅔. Untick to enter true decimal innings such as 6.333.

9 for standard baseball; 7 is common in softball and many youth and high-school leagues.

Result

Earned run average

2.99

60 earned runs over 180.667 innings is an ERA of 2.99.

Innings as a decimal
180.667
Outs recorded
542
Earned runs per inning
0.332

See the step-by-step solution ↓

Step-by-step solution

  1. Convert the notation: the digit after the point counts outs, and each out is one third of an inning

    180.2 IP=180 ⅔ innings=180×3+23=180.666667

  2. ERA scales earned runs to a 9-inning game: 9 times earned runs, divided by innings pitched

    ERA=9×ERIP

  3. Put in your earned runs and true innings to get the ERA

    9×60180.666667=540180.666667=2.98893

Test yourself

20 quick questions built from this calculator's formula: work out results, predict what happens when an input changes, and work backward from an answer. Every answer comes with the working.

What this calculator does

Find a pitcher's earned run average (ERA): how many earned runs they allow over a full game. Pitchers throw very different numbers of innings, so raw run totals are hard to compare. Scaling them to nine innings puts a starter with 200 innings and a reliever with 60 on the same footing.

The catch is the way innings are written. An out is a third of an inning, so scorebooks write 6⅓ innings as 6.1 and 6⅔ as 6.2. Typing 6.1 straight into a formula as six and one-tenth gives the wrong answer. This calculator reads the notation correctly by default, shows the conversion in the working, and can add WHIP (walks plus hits per inning) as well.

Where it's used

Why this math matters outside the classroom:

  • Runs per nine innings. A pitcher who allows 3 earned runs in 6⅓ innings has an ERA of 9 × 3 ÷ 6⅓, which is about 4.26.
  • Innings in thirds. Scorekeepers read 6.2 innings in a box score as 6⅔, since each out is one third of an inning.
  • Season stats. Coaches add up earned runs and innings across a season to compare their pitchers' ERAs on one sheet.
  • Shorter games. Softball and youth leagues with 7-inning games multiply by 7 instead of 9 to get an ERA on their own scale.
  • WHIP alongside ERA. Fans pair ERA with WHIP, walks plus hits divided by innings, to see how often a pitcher lets runners reach base.

Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 7.RP.A.1, 6.RP.A.3.b. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.

How to use it

  1. Enter earned runs allowed. Unearned runs, those that score only because of a fielding error or passed ball, are left out.
  2. Enter innings pitched as they appear in the box score, such as 180.2. Leave the notation box ticked so .1 and .2 are read as one and two outs.
  3. Change the game length to 7 for softball or a 7-inning league if needed.
  4. Optionally add walks and hits allowed to see WHIP too.

What the inputs mean

Innings pitched (IP)
With notation on, only .0, .1 and .2 are valid after the point, because a third out ends the inning. Untick the box if your figure is already a true decimal such as 6.333.
Innings use baseball notation (.1 = ⅓ inning, .2 = ⅔ inning)
6.1 means six full innings plus one out, which is 6⅓ or about 6.333 innings, not 6.1. The calculator converts to outs (6 × 3 + 1 = 19) and divides by 3.
Innings in a regulation game
The number of innings ERA is scaled to. It is 9 for standard baseball; many softball, high-school and youth leagues play 7.
Walks allowed (optional, for WHIP)
Optional. Enter both walks and hits allowed to get WHIP; leave either blank to skip it.

Formula and method

true innings = (whole innings × 3 + extra outs) ÷ 3
ERA = game length × ER ÷ IP
WHIP = (BB + H) ÷ IP

In the formulas, ER is earned runs, IP is innings pitched, BB is walks (bases on balls) and H is hits allowed. ERA is earned runs per inning multiplied by the innings in a regulation game. With a nine-inning game it is 9 × ER ÷ IP.

Innings must be a true number before dividing, so the notation is converted to outs and back to thirds first. WHIP uses the same corrected innings.

Worked example

A starting pitcher allows 60 earned runs in 180.2 innings.

  1. Convert the notation: 180.2 is 180 innings and 2 outs, or (180 × 3 + 2) ÷ 3 = 542 ÷ 3 = 180.666667 innings.
  2. Multiply earned runs by 9: 9 × 60 = 540.
  3. Divide by the true innings: 540 ÷ 180.666667 = 2.988930.

Result: The ERA is 2.99. Reading 180.2 as a plain decimal would give about 2.997 instead; the gap is small over a season but large over a few innings.

Understanding the result

Lower is better. In professional baseball an ERA under about 3.00 is generally excellent, around 4.00 is ordinary, and above 5.00 is poor, though the league norm shifts from year to year.

Short stints exaggerate everything. A reliever who gives up two earned runs while recording a single out has an ERA of 54.00 for that outing.

Assumptions and limitations

  • Earned and unearned runs have already been separated by the official scorer.
  • Innings are entered either in thirds notation or as true decimals, as chosen by the checkbox.
  • ERA depends on the fielders behind the pitcher and on the scorer's judgment of errors. It is not adjusted for ballpark or league.
  • Zero innings pitched is not accepted: a pitcher who allows runs without recording an out has an undefined ERA.

Frequently asked questions

Why is 6.1 innings not six and one-tenth?

Innings are counted in outs, three to an inning. Box scores put the number of extra outs after the decimal point, so 6.1 means one extra out (6⅓ innings) and 6.2 means two (6⅔). There is never a 6.3, because the third out completes the seventh inning.

What makes a run earned?

A run is earned if it would have scored without fielding errors or passed balls. The official scorer reconstructs the inning as if it had been played cleanly; runs that score only because of a misplay are unearned and do not count toward ERA.

What is WHIP?

Walks plus hits per inning pitched. It measures how many runners a pitcher lets on rather than how many score, so it is less dependent on what happens after a runner reaches base.

How do I calculate ERA for softball?

Set the game length to 7. The formula becomes 7 × earned runs ÷ innings pitched, matching the shorter regulation game.

How this calculator is checked

Method: Standard scorekeeping definitions of earned run average (game length × ER ÷ IP) and WHIP; innings-in-thirds notation per common box-score convention. The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.

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