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K/9 Calculator (Strikeouts per 9 Innings)

Calculate a pitcher’s K/9 (strikeouts per nine innings) plus BB/9, H/9, HR/9, K/BB, strikeout rate and K−BB% from innings pitched and season totals.

Innings pitched

Strikeouts (K)

Walks (BB)

Hits allowed

Home runs allowed

Batters faced (optional)

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How it works

K/9 = strikeouts × 9 ÷ innings pitched · BB/9, H/9 and HR/9 use the same × 9 ÷ IP form · K/BB = K ÷ BB · K% = K ÷ batters faced · K−BB% = (K − BB) ÷ batters faced.

K/9 scales a pitcher’s strikeouts to a full nine-inning game so pitchers with different workloads can be compared. FanGraphs’ classic rule of thumb calls 10.0 excellent, 7.7 average and 5.0 awful, although league strikeout rates have climbed and the MLB average has been about 8.5–8.8 in recent seasons. Because K/9 also rises when a pitcher allows more baserunners (more batters per inning), analysts increasingly prefer K% and K−BB%, which this calculator adds when you enter batters faced.

Worked example

A starter with 190 strikeouts, 50 walks, 160 hits and 20 home runs in 180 innings: K/9 = 190 × 9 ÷ 180 = 9.50 (Great), BB/9 = 2.50, K/BB = 3.80, H/9 = 8.00 and HR/9 = 1.00. Against 740 batters faced his K% is 25.7% and K−BB% is 18.9%.

Sources: FanGraphs Sabermetrics Library — Rate stats (K/9, BB/9) · MLB.com Glossary — Strikeouts per 9 innings (K/9)

Frequently asked questions

How do you calculate K/9?

Multiply strikeouts by 9 and divide by innings pitched. 190 strikeouts in 180 innings is 190 × 9 ÷ 180 = 9.50 strikeouts per nine innings.

What is a good K/9?

Around 9 or more is very good and 10+ is elite; the MLB average has been roughly 8.5–8.8 in recent seasons. Relievers usually post higher K/9 than starters because they throw at full effort for short stints.

Is K% better than K/9?

Usually yes. K/9 goes up if a pitcher faces more batters per inning, even though that is bad. K% divides by batters faced, so it measures pure strikeout ability; K−BB% is one of the best simple predictors of future ERA.

What is a good K/BB ratio?

A strikeout-to-walk ratio of 3.0 or better is good, 4.0+ is excellent, and under 2.0 suggests control problems.

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This calculator is for educational purposes. Double-check important results before acting on them.