K/9 Calculator
Calculate strikeouts per nine innings (K/9) from strikeouts and innings pitched.
Informational only — not a substitute for official league statistics or professional judgment.
How it's calculated
Assumptions
- Uses nine innings by definition — K/9 is always expressed per nine innings regardless of a league's game length.
- Innings pitched must be entered in standard baseball notation (.0, .1, or .2 for 0, 1, or 2 outs) — not tenths of an inning.
Source: MLB Glossary — Strikeouts per Nine Innings (K/9)
Last reviewed: July 2026
Frequently asked questions
What's considered a good K/9?
In recent MLB seasons the league-average K/9 has sat in the high 8s. Around 9.0 is solid for a starter, 10.0+ is a legitimate strikeout pitcher, and 11.0+ is elite territory usually reserved for top starters and late-inning relievers.
Why does innings pitched use .1 and .2 instead of normal decimals?
Baseball box scores record partial innings in thirds, not tenths: .1 means one out recorded (1/3 of an inning) and .2 means two outs recorded (2/3 of an inning). This calculator converts that notation to real innings automatically before computing K/9.
How is K/9 different from strikeout percentage (K%)?
K/9 counts strikeouts per nine innings, while K% counts strikeouts per batter faced. Analysts increasingly prefer K% because a pitcher who allows lots of baserunners faces more batters per inning, which inflates their K/9 without them actually striking out a higher share of hitters.
What is K/9 IP as a stat abbreviation — is SO/9 the same thing?
Yes. K/9, SO/9, and SO9 all refer to the same stat: strikeouts per nine innings pitched. K is the scorekeeping symbol for a strikeout, and different sites simply abbreviate the stat differently.
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