Earned run average is earned runs multiplied by the innings in a regulation game, divided by innings pitched. Partial innings count as thirds, so 304.2 innings is 304⅔. Bob Gibson allowed 38 earned runs in 304.2 innings in 1968: 38 × 9 ÷ 304.667 = 1.12.
Coaches, scorekeepers, fantasy players and parents tracking a season often have a pitcher's line from each game and want the season ERA without fumbling the thirds of an inning. Enter one row per outing with full innings, the extra outs in an unfinished inning, and the earned runs charged. The result gives the combined ERA, total innings in box-score notation, earned runs per inning, a per-outing table and a bar chart comparing each outing with the total. Pick 7 or 6 innings for high school or youth games, where ERA is scaled to the shorter game. Deciding which runs are earned is the official scorer's call under the rules on errors and passed balls; this calculator takes that number as given.
Type the full innings completed, then 0, 1 or 2 extra outs. A box score's 5.2 means 5 full innings and 2 extra outs.
Use the earned runs from the box score, not total runs; unearned runs are left out of ERA.
Leave 9 for MLB and college, or pick 7 for high school and 6 for many youth leagues.
The table lists each outing's own ERA, and the bar chart sets them beside the combined figure.
Result Earned run average: 1.12
Innings pitched: 304.2
Earned runs: 38
Earned runs per inning: 0.125
Rough MLB-level rating: Elite
304 and two-thirds innings with 38 earned runs gives the 1.12 ERA that is still the live-ball record for a qualified starter.
Result Earned run average: 3.97
Innings pitched: 11.1
Earned runs: 5
Earned runs per inning: 0.441
Rough MLB-level rating: Around average
Five earned runs over 34 outs works out to 3.97; the 5.1 means five innings and one out, not 5.1 innings.
Result Earned run average: 3.00
Innings pitched: 7.0
Earned runs: 3
Earned runs per inning: 0.429
Rough MLB-level rating: Above average
Three earned runs over a full seven-inning game is an ERA of 3.00 on the seven-inning scale.
ERA = ER × G ÷ IP, where IP = full innings + outs ÷ 3
ERGIPAll outings are converted to outs first, summed, and divided by 3 to get innings pitched, which avoids the common error of treating 5.1 as five and one tenth. Earned runs are summed separately. The season ERA is the total earned runs scaled to a full game, not the average of the per-outing ERAs, so long outings weigh more than short ones.
An earned run is any run that scores without the help of a fielding error or a passed ball, as judged by the official scorer. If an error extends an inning, runs that would not have scored without it are unearned, even when the pitcher allows more hits afterwards.
Box scores record outs, not decimal innings. Each inning has three outs, so the digit after the point is the number of extra outs: .1 is one out (a third of an inning) and .2 is two outs. There is never a .3.
League-wide MLB ERA has sat roughly between 3.8 and 4.5 in recent seasons. Under 3.00 is excellent for a starter, around 4.00 is about average and above 5.00 is poor. The rating shown here uses those rough bands and is meant for nine-inning professional ball.
High school and some softball and youth leagues multiply earned runs per inning by 7 instead of 9, so the figure reflects runs allowed over a full game at that level. The same pitching line gives a lower number on the 7-inning scale.
Yes, in record books a pitcher who allows earned runs without recording an out has an infinite ERA. This calculator asks for at least one out, since dividing by zero innings gives no number.
Season ERA divides total earned runs by total innings. A one-inning outing with three runs has a 27.00 game ERA but adds little to the season total compared with a seven-inning start.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 26). Baseball Earned Run Average. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/sports/running-and-endurance/baseball-earned-run-average/
Tools Directory Editorial Team. “Baseball Earned Run Average.” Tools Directory, 26 Oct. 2026, https://tools.milunir.com/sports/running-and-endurance/baseball-earned-run-average/. Accessed 26 Oct. 2026.
Tools Directory Editorial Team. “Baseball Earned Run Average.” Tools Directory. Last modified October 26, 2026. Accessed October 26, 2026. https://tools.milunir.com/sports/running-and-endurance/baseball-earned-run-average/.
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