These three metrics measure a pitcher’s core skills relative to the innings he throws, which makes it fair to compare starters and relievers: how much he strikes out, how much he gives away, and the relationship between the two.
What each one measures
- K/9 (strikeouts per 9 innings): dominance. The higher it is, the more hitters he retires on his own.
- BB/9 (walks per 9 innings): control. The lower it is, the fewer free runners he gives away.
- K/BB (strikeout-to-walk ratio): the relationship between the two; it sums up dominance and control in a single number.
Benchmark values
| Metric | Very good |
|---|---|
| K/9 | 10 or higher |
| BB/9 | Under 2.5 |
| K/BB | 4 or higher |
Why they matter
A pitcher who strikes out a lot and gives up few walks controls the game without relying on his defense. That’s why K/BB is one of the best indicators of quality and sustainable performance.
[Live data — MLB API] Current-season K/9 and K/BB leaders: (filled in automatically).
Related stats
Frequently asked questions
What K/9 is good?
10 or higher is the sign of a pitcher who dominates with strikeouts.
Why divide by 9 innings?
So you can fairly compare pitchers who throw different numbers of innings.
