Capability (or Process Capability, or Cpk)

The level of ability involved with a process to perform as expected. Often referred to as Cpk, this reflects how well a process can be performed and delivered defect free. The Cpk is compared to ‘1.00’ as a measure of how ‘good’ a process is in performing to expectation.

  • A Cpk < 1.00 indicates a process with variation that exceeds a specified expected performance window.
  • A Cpk = 1.00 indicates that 99.9% performance falls within a specified expected performance window.
  • A Cpk > 1.00 indicates a process with tight variation around its mean. It performs consistently better than a specified expected performance window.

A process with a Cpk = 2.00 is equivalent to a Six Sigma level performance, or 3.4 defective parts per million parts.

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