Process capability index (Cpk) is a statistical tool, to measure the ability of a processto produce output within customer's specification limits. In simple words, it measures producer's capability to produce a product within customer's tolerance range.
cpk = min(Cpu , Cpl)
= min
given usl = 6, ,
Cpk = min
= min ()
= min ( 1.3 , 2.6)
cpk = 1.3
Cpk = or >1.33 indicates that the process is capable and meets specification limits. Any value less than this may mean variation is too wide compared to the specification or the process average is away from the target.