K/9 is strikeouts multiplied by 9, divided by innings pitched, where the digit after the dot counts outs, not tenths. Gerrit Cole struck out 326 batters in 212.1 innings in 2019: 326 × 9 ÷ 212.333 = 13.82 K/9. A league-average starter usually sits somewhere around 8 to 9.
Scouts, fantasy players and coaches use K/9 to compare how often pitchers miss bats, regardless of how many innings each one threw. The catch is the box-score innings figure: 6.2 means six innings and two outs, which is 6.667 innings, so typing 6.2 into an ordinary division gives the wrong rate. This calculator takes full innings and the extra outs separately, then reports K/9, strikeouts per inning, total outs recorded and the share of those outs that came by strikeout. It also flags samples under ten innings, where one strikeout moves the rate a lot. It does not adjust for park, league or opponent, and it says nothing about walks or contact quality, so read it next to K/BB or strikeout percentage per batter faced.
Type the pitcher's strikeout total for the game, season or career span you want to rate.
Use the number before the dot in the innings-pitched column, for example 212 from 212.1.
Choose .0, .1 or .2 to match the digit after the dot; each one is a third of an inning.
K/9 appears with strikeouts per inning, outs recorded and the strikeout share of outs, plus the working.
Result K/9 (strikeouts per nine innings): 13.82
Innings pitched: 212.1 (212.333 innings)
Strikeouts per inning: 1.535
Outs recorded: 637
Strikeouts as a share of outs: 51.2%
Gerrit Cole's 2019 season. The .1 means one out, so the divisor is 212 1/3 innings, not 212.1.
Result K/9 (strikeouts per nine innings): 11.48
Innings pitched: 211.2 (211.667 innings)
Strikeouts per inning: 1.276
Outs recorded: 635
Strikeouts as a share of outs: 42.5%
Nolan Ryan led the National League in 1987; two extra outs make the innings 211 2/3.
Result K/9 (strikeouts per nine innings): 13.50
Innings pitched: 2.0 (2 innings)
Strikeouts per inning: 1.5
Outs recorded: 6
Strikeouts as a share of outs: 50%
A reliever's two-inning outing. The rate looks elite, but six outs is far too few to judge a pitcher by.
K/9 = K × 9 ÷ IP, where IP = full innings + outs ÷ 3
KIPoutsBaseball scores partial innings in thirds, so the box-score notation 212.1 is converted to 212 + 1/3 before dividing. Multiplying by 9 scales the rate to a regulation game. Strikeouts per inning is K ÷ IP, and the strikeout share of outs is K ÷ (IP × 3); strikeouts on dropped third strikes can push that share past 100% in rare cases.
In recent Major League seasons the league average has been close to 8.5 to 9 strikeouts per nine innings. Starters above 10 are among the better strikeout pitchers, and elite seasons such as Gerrit Cole's 13.82 in 2019 are rare. Relievers routinely post higher figures because they throw at full effort for short stints.
Each inning has three outs, so box scores write one out as .1 and two outs as .2. Six innings and one out is 6 1/3, or 6.333 innings. Treating it as 6.1 understates the innings slightly and inflates K/9.
K/9 divides by innings, so a pitcher who allows many baserunners faces more batters per inning and gets more chances to strike someone out. Strikeout percentage divides by batters faced and removes that effect, which is why many analysts now prefer it for comparing pitchers.
Yes, though rarely. If a batter reaches base on a dropped third strike, the pitcher gets a strikeout without recording an out. Over an inning with several of those, strikeouts can outnumber outs, and the calculator shows a warning when that happens.
Yes. Baseball-Reference labels the stat SO9 and FanGraphs labels it K/9; both multiply strikeouts by nine and divide by innings pitched counted in thirds. Their displayed figure may show one decimal where this page shows two.
The formula still works, but scaling to nine innings makes less sense when games are seven innings long. Some softball and youth leagues quote K/7 instead, which is the K/9 figure multiplied by 7 ÷ 9.
Using this tool in an assignment, article or report? Copy a citation, or a link for your website.
Tools Directory Editorial Team. (2026, October 15). K/9 Calculator. Tools Directory. Retrieved October 26, 2026, from https://tools.milunir.com/sports/sports-performance/k9-calculator/
Tools Directory Editorial Team. “K/9 Calculator.” Tools Directory, 15 Oct. 2026, https://tools.milunir.com/sports/sports-performance/k9-calculator/. Accessed 26 Oct. 2026.
Tools Directory Editorial Team. “K/9 Calculator.” Tools Directory. Last modified October 15, 2026. Accessed October 26, 2026. https://tools.milunir.com/sports/sports-performance/k9-calculator/.
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