200 strikeouts in 180.1 innings is a K/9 of 9.98
K/9 is the number of strikeouts a pitcher records per nine innings. The formula is strikeouts × 9 ÷ innings pitched, with one catch: the .1 and .2 at the end of an innings total are not decimals but the extra outs recorded in that inning. So 180.1 innings means 180⅓ innings, or 541 outs. Convert to outs and the formula becomes strikeouts × 27 ÷ outs, which gives 200 × 27 ÷ 541 = 9.98 for 200 strikeouts.
That 9.98 is 1.49 above the 2025 MLB average of 8.49. The same year's NPB average was 7.29 and the KBO average 7.77, so the same K/9 sits at a different distance from the average depending on the league. The calculator above fills in how many of the 27 outs in nine innings are strikeouts and sets that beside the average of the league you pick.
What K/9 tells you
- Strikeout ability: a strikeout is an out that needs no help from the defense, which makes it a standard measure of a pitcher's own stuff.
- Pitchers with different workloads: raw strikeout totals favor whoever threw more. Dividing by nine innings puts a starter's 30 outings and a reliever's 60 on the same scale.
- Trends within a season: comparing the last few starts with the full-season K/9 hints at whether a pitcher's stuff is rising or fading. With few innings, though, one or two strikeouts swing the number a lot.
How it is calculated
- Innings to outs: whole innings × 3 plus the last digit (.1 is 1, .2 is 2). 180.1 innings = 180 × 3 + 1 = 541 outs.
- K/9: strikeouts × 27 ÷ outs (the same as strikeouts × 9 ÷ true innings), shown rounded to two decimals.
- BB/9 and K/BB: walks × 27 ÷ outs, and strikeouts ÷ walks.
- K%, BB% and K−BB%: strikeouts ÷ batters faced, walks ÷ batters faced, and the difference between the two.
- League average: add up every pitcher's strikeouts, walks, outs and batters faced in that league, then apply the same formulas (it is not a simple average of individual K/9 figures).
| As written | Actual innings | Outs |
|---|---|---|
| 6 | 6 | 18 |
| 6.1 | 6⅓ | 19 |
| 6.2 | 6⅔ | 20 |
| 180.1 | 180⅓ | 541 |
| 6.3 | Not a valid entry (it is 7 innings) | - |
2025 league averages
These come from the 2025 regular-season pitching totals of each league. The 2026 KBO regular season had not finished as of 2026-10-12, so all three leagues are set to 2025.
| League | Strikeouts | Innings | K/9 | BB/9 | K% | BB% |
|---|---|---|---|---|---|---|
| KBO | 11,024 | 12,773⅔ | 7.77 | 3.61 | 19.7% | 9.1% |
| MLB | 40,645 | 43,075 | 8.49 | 3.21 | 22.2% | 8.4% |
| NPB | 12,475 | 15,392⅓ | 7.29 | 2.67 | 19.4% | 7.1% |
Basis: 2025 regular season (postseason excluded). League totals from Baseball-Reference, the ten-team sum of KBO team pitching records and the twelve-team sum of npb.jp team pitching stats, checked on 2026-10-12. The KBO regular season had not finished that day, so all three leagues are set to 2025.
MLB is highest and NPB lowest, so the league averages alone differ in K/9 by about 1.2. KBO has a K% close to NPB's but the highest BB/9. When you look at a pitcher who moved between leagues, the distance from his league's average tells you more than the raw number.
FanGraphs rough tiers
The FanGraphs Library gives rough benchmarks like these for strikeout and walk rates. The table was written in 2010 around MLB, and FanGraphs notes that league averages change every year. This calculator places a result in a tier when it meets the value (or, for walk measures, falls at or below it).
| Tier | K/9 | K% | BB/9 | BB% |
|---|---|---|---|---|
| Excellent | 10.0 | 27% | 1.5 | 4.5% |
| Great | 9.0 | 24% | 1.9 | 5.5% |
| Above average | 8.2 | 22% | 2.5 | 6.5% |
| Average | 7.7 | 20% | 2.9 | 7.7% |
| Below average | 7.0 | 17% | 3.2 | 8.0% |
| Poor | 6.0 | 15% | 3.5 | 8.5% |
| Awful | 5.0 | 13% | 4.0 | 9.0% |
The 2025 MLB average K/9 of 8.49 lands in "Above average" on this table. That shows how much strikeouts have risen since 2010, so treat the tiers as a rough ruler and judge by the gap to the league average instead.
K/9 versus K%
K/9 is based on outs, K% on batters faced. FanGraphs gives the example of two pitchers who each strike out two batters in an inning, one facing six batters and the other three. Both have a K/9 of 18.0, yet their K% is 33% and 66%. A pitcher who lets many runners on faces more batters every inning, which can inflate his K/9, so K% is the more accurate measure when comparing pitchers. Enter batters faced and the calculator shows K% too.
Common mistakes
Treating the last digit of the innings as a decimal makes the divisor smaller than the real innings, so K/9 comes out too high. The fewer the innings, the bigger the error.
| Strikeouts | Innings as written | Correct K/9 | Treated as a decimal |
|---|---|---|---|
| 8 | 5.1 | 13.50 | 14.12 |
| 20 | 12.2 | 14.21 | 14.75 |
| 65 | 50.1 | 11.62 | 11.68 |
| 200 | 180.1 | 9.98 | 9.99 |
- Innings ending in .3 or higher: three outs make the next full inning, so write 7, not 6.3.
- Comparing starters and relievers on one scale: FanGraphs says relievers tend to post a K% about 3 percentage points higher than starters.
- Mixing leagues: an 8.0 K/9 is below the MLB average, but in NPB the same 8.0 is more than 0.7 above the average.
- Judging from a few games: in a single inning, one strikeout moves K/9 by 9.
Limits and cautions
- K/9 looks only at strikeouts and outs. It ignores walks, hits, home runs allowed, the quality of opposing lineups and ballparks. Read it next to BB/9 and measures like FIP to judge run-prevention risk.
- League averages are regular-season totals for 2025 and leave out the postseason. Averages change from year to year, so check that the average is from the same year as the stats you are comparing.
- The FanGraphs tiers are benchmarks written in 2010 with MLB in mind, and they sit low for today's leagues. That is why the comparison next to the result is against the league average.
- A strikeout is credited even when the batter reaches base on a dropped third strike, so on rare occasions strikeouts can exceed outs. The calculator computes that case as entered.
Sources
- 01FanGraphs Library: Strikeout and Walk RatesRough tables for K/9, K%, BB/9 and BB% (2010-02-19), league averages change every year, relievers' K% about 3 points higher, why K% is more useful for comparison
- 02Baseball-Reference: 2025 Major League Baseball PitchingMLB 2025 league totals: 43,075 innings, 40,645 strikeouts, 15,379 walks, 182,926 batters faced
- 03KBO Records: Team Pitching (2025 regular season)Ten-team totals: 12,773⅔ innings, 11,024 strikeouts, 5,123 walks, 55,996 batters faced (Basic2)
- 04NPB: 2025 Central League team pitchingTwelve-team totals with the Pacific League (tmp_p.html): 15,392⅓ innings, 12,475 strikeouts (三振), 4,559 walks (四球), 64,178 batters faced (打者)
Frequently asked questions
How do you calculate K/9?
Strikeouts × 9 ÷ innings pitched. Because the .1 and .2 in innings mean ⅓ and ⅔ of an inning, converting to outs gives strikeouts × 27 ÷ outs. With 200 strikeouts in 180.1 innings (541 outs) it is 200 × 27 ÷ 541 = 9.98.
Can I just divide by 180.1 as it is written?
No. 180.1 means 180⅓ innings, so the .1 is 0.333… of an inning, not 0.1. With many innings the gap is small, but for 8 strikeouts in 5.1 innings the correct K/9 is 13.50, while dividing by 5.1 gives 14.12.
What is a good K/9?
It depends on the league. The 2025 regular-season averages were 8.49 in MLB, 7.77 in KBO and 7.29 in NPB. FanGraphs offers a rough table written in 2010 with MLB in mind (10.0 excellent, 9.0 great, 7.7 average), and notes that league averages change every year.
Should I look at K/9 or K%?
For comparing pitchers, K% is better. FanGraphs explains that weaker pitchers face more batters per inning, so K%, the share of batters faced who strike out, is more useful than a rate based on outs. Enter batters faced and the calculator gives K% too.
What is the 2025 KBO average K/9?
Adding the 2025 regular-season pitching lines of the ten teams on the official KBO records site gives 11,024 strikeouts in 12,773⅔ innings, a K/9 of 7.77. The same totals give a BB/9 of 3.61, a K% of 19.7% and a BB% of 9.1%.
Can I compare starters and relievers directly?
Be careful. FanGraphs says relievers tend to post a K% about 3 percentage points higher than starters. A reliever pitching short stints can go all out, so the same K/9 means something different.
What are K/BB and K−BB%?
K/BB is strikeouts ÷ walks, and K−BB% is K% minus BB%. Strikeouts alone can mislead if a pitcher also walks many batters, so these measures look at both together. With 0 walks, K/BB is not calculated.
Can I trust K/9 over few innings?
It swings a lot. In a single inning, one extra strikeout moves K/9 by 9. Early in a season or just after an injury return, look at cumulative innings and batters faced as well.