**Process Capability (Cp)** **and Performance (Cpk)**

## What does CP and Cpk tell you?

The Cp and Cpk indices are the primary capability indices. **Cp shows whether the distribution can potentially fit inside the specification, while Cpk shows whether the overall average is centrally located**. If the overall average is in the center of the specification, the Cp and Cpk values will be the same.

## What does it mean when CP is higher than Cpk?

When Cp is greater than Cpk, **the mean is nearer to one specification limit or the other**. Once you understand your process, you can make a good decision about how to prioritize your process improvement efforts.

## What does a Cpk of 1.33 mean?

A CpK of 1.33 means that **the difference between the mean and specification limit is 4σ** (since 1.33 is 4/3). With a CpK of 1.33, 99.994% of the product is within specification. Similarly a CpK of 2.0 is 6σ between the mean and specification limit (since 2.0 is 6/3).

## What does a Cpk of 1.67 mean?

Excellent, Capable

The Capability Index, Cpk.

The outcome of a Process Capability study is a single metric, which provides an indication of the ability of a process to consistently provide output which is within required specifications. CPK <1.00 (Poor, incapable) 1.00< CPK <1.67 (Fair) CPK >1.67 (**Excellent, Capable**)

## Is a higher or lower Cpk better?

**The higher the Cpk, the better is the capability of the process to meet its requirements**. In the industry, a Cpk of less than 1.66 needs a closer look. A Cpk that’s less than 1.33 needs some action to make it higher, and a Cpk of less than 1.0 means that the process is not capable of meeting its requirements.

## What if Cpk is lower than CP?

If Cpk is less than Cp and Cp is greater than one, **center the process in the specification**. This should make Cpk comparable to Cp.

## What if CP is greater than 1?

A Cp of greater than one indicates that **the process spread is less than the width of the specification**. Potentially this means that the process can fit inside the specification limits.

## What does a Cpk of 1.4 mean?

A Cpk of 1.4 equates to **a sigma level of 4.2 and a defect rate of less than 0.0027%**. If there is significant bias then only one tail of the distribution will causing a significant chance of defects and so the defect rate may be only half this value.

## What does a high CP value mean?

What is Cpk (Simple Explanation of Cp and Cpk)

## What can be concluded when CP equals Cpk?

If Cp and Cpk are approximately equal, then **the process is centered between the specification limits**. If Cp and Cpk differ, then the process is not centered.

## What does a Cpk of 1.4 mean?

A Cpk of 1.4 equates to **a sigma level of 4.2 and a defect rate of less than 0.0027%**. If there is significant bias then only one tail of the distribution will causing a significant chance of defects and so the defect rate may be only half this value.

## What should be the CP and Cpk values for Six Sigma?

According to Six Sigma philosophy, Cp or Pp and Cpk or Ppk should be **greater than 1.50**. From a technical standpoint, Six Sigma deems a process being acceptable only after achieving a maximum defect rate of 3.4 parts per million opportunities.