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What Does K/9 Mean in Baseball? (Strikeouts per Nine Innings)


Written by

A. Coatess


Fact checked by

Sean Hunter

what does k9 mean in baseball

Statistics help assess player attributes in baseball. There are stats relevant to each position, such as the K/9 and H/9 pitching metrics. What does K/9 mean in baseball? What does K 9 stand for, and why is it a good measure of pitching prowess?

K/9 refers to the average number of strikeouts a pitcher achieves per nine innings of baseball. It is among the most celebrated pitcher stats because it means throwing hitters out.

What is a Strikeout in Baseball?


To understand the K 9 meaning better, let us first learn what a strikeout means in baseball.

A strikeout happens when the pitcher sends the batter out, thereby preventing the latter from scoring runs. This feat is indicated with a “K” in baseball score sheets.

The most common scenario for a strikeout is when the batter accumulates a combination of three unsuccessful swings and missed strikes during an at-bat. If the catcher secures the third strike before the ball hits the ground, the batter is automatically put out.

A strikeout may also arise from a fielder’s choice when there are runners on all bases. For instance, if the catcher fails to catch the third strike on the fly, he may opt to put out the third-base runner by stepping on the home plate instead of fielding the ball to first base.

Another thing worth mentioning is that a strikeout is specifically recorded as “strikeout looking” if the batter lets the third strike pass without attempting to swing at the ball. Such a scenario is indicated with a reverse K on the scorecard.

Along with the bases-on-ball stat (BB%), strikeouts (K%) are the best indicators of pitching prowess. The ideal combination is a high K% and a low BB%; a quick look at both stats will tell you how good a pitcher is.

Now that you know the K 9 definition in detail, let us discuss how this stat is calculated.

How Do You Calculate the K/9 Ratio?


K/9 MLB figures are indicated in decimals and derived in two ways. First, you can divide the number of strikeouts a pitcher has generated by the number of innings they have pitched during their career and multiply the result by nine.

You can also calculate K/9 in baseball by multiplying the total number of strikeouts by nine and then dividing the result by the total number of innings pitched.

Let’s look at a specific example and use both formulas to get the K per 9 percentage. For instance, player A pitched a total of 1200 innings and attained 950 strikeouts over his career.

Formula 1:

(Total Strikeouts ÷ Total Innings) x 9 = K/9 ratio
(950 ÷ 1200) x 9 = 7.12

Formula 2:

(Total Strikeouts x 9) ÷ Total Innings = K/9 ratio
(950 x 9) ÷ 1200 = 7.12

Hence, player A has an average of 7.12 strikeouts per 9 innings pitched. You can validate these results using a strikeout per 9 innings calculator. Look for an online k/9 calculator and input the above stats.

Chris Sale of the Boston Red Sox and Robbie Ray of the Seattle Mariners lead the list of all-time MLB K/9 leaders with an 11.07 and 11.03 K/9 rate, respectively. Both pitchers are lefties.

What Are the H/9 and Bb/9 MLB Stats?


H/9 stands for the average number of hits allowed by a pitcher per nine innings. It is calculated by dividing all hits by the number of innings pitched and multiplying the resulting figure by nine.

A good understanding of the H/9 meaning will tell you how often batters get to hit the ball. Remember that a pitcher’s main job is to prevent hits and runs.

In contrast, the BB/9 baseball stat represents the average number of walks a pitcher allows per nine innings. A lower figure is more desirable since a walk to base is considered an embarrassment for both the pitcher and batter.

A rating of 2 or below is a good BB/9 in baseball, while 1.5 is considered excellent.


A quick look at statistics can help you assess player performance in baseball. Pitchers with impressive K/9 ratings are known to send hitters back to the dugout even before the ball goes into play.

What does K/9 mean in baseball? You know now that it represents the average number of strikeouts a pitcher is credited with per nine innings of baseball. Share your knowledge with other fans so they can tell apart an average and highly-skilled MLB pitcher.

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