K/9 = (Strikeouts × 9) / IP, with BB/9 computed the same way.
K/9 above 9 is strong; 12+ is elite. BB/9 under 2.0 is ideal.
K/BB ratio is also useful (above 3.0 is good, 5.0+ is elite).
Yu Darvish led the AL with 277 strikeouts in 2013, posting an 11.9 K/9.