# Process Capability Analysis in Excel

## You Don't Have to be a Black Belt to Perform Capability Analysis

A capable process meets customer requirements 100% of the time. Customer requirements are defined using an upper specification limit (USL) and a lower specification limit (LSL). Think of these specification limits as goal posts.

Not Capable |
Capable |
---|---|

Cp < 1, Cpk <1 |
Cp >= 1, Cpk >= 1 |

Not Capable to Centered & Capable |
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**Process capability metrics** are used to determine how well the output of a stable process meets these specifications:

## Cp and Cpk |
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Cp measures how well the data would fit within the spec limits (USL, LSL) |

Cpk measures how centered the data is between the spec limits. |

Use Cp Cpk when you have a sample, not the population, and are testing the potential capability of a process to meet customer needs. |

Cp and Cpk use Sigma estimator. |

## Pp and Ppk |
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Pp measures how well the data would fit within the spec limits (USL, LSL) |

Ppk measures how centered the data is between the spec limits. |

Use Pp Ppk when you have the total population and are testing the performance of a system to meet customer needs. |

Pp, Ppk use standard deviation. |

### Cp vs Cpk Examples

## Fits But Is Not Centered |

Process improvement goal is to make changes that will move the output closer to the target without increasing variation. |

## Centered But Does Not Fit |

Process improvement goal is to reduce variation so that the process fits between the spec limits. |

### One-sided Spec Limits

## One-Sided Spec Limit |

Sometimes, people think a "hard limit," such as zero, is a "spec limit".
In this case, Cpk uses CpkU which means Cpk > 1. |

## One-Sided Spec Limit |

If you enter an LSL of zero, Cpk uses CpkL which means Cpk < 1 because the mean is closer to zero. |

### Capability Analysis Metrics Rules of Thumb

**Cp > 1**Process is capable (product will fit between the customer's upper and lower specification limits if the process is centered).**Cpk > 1**Process is capable and centered between the LSL and USL.- If Cp = Cpk the process is centered at the midpoint of the specification limits.
- If Cp > Cpk the process is off-center.
- Cp and Cpk should be close in value to Pp and Ppk.
- If Cp and Cpk are much greater than Pp or Ppk (
*33% greater*), your process may not be stable enough to conduct a capability analysis. Use control charts to evaluate the stability of your process.

### Why Choose QI Macros Capability Software?

#### Are You New to Capability Analysis?

QIMacros Capability Tools Eliminate the Learning Curve!

Calculations for Cp, Cpk, Pp and Ppk are built right into our code so you don't have to learn any complex formulas. Just select the data, choose a chart from our pull down menu and enter your specification limits.

#### Are You Already Using Capability Analysis?

If you already know what chart you want, just select the data and click on one of the QI Macros Capability Tools. We do the math and draw the graph. The Capability Suite gives you a control chart and histogram to compliment Cp and Cpk. Histograms give Cp and Cpk. You can even do Weibull analysis. And You can email your charts to anyone who has Excel. You can copy and paste them into PowerPoint or Word.

#### Is Most Your Data In Excel?

QIMacros
Works *Inside* Microsoft Excel

You don't need to learn a separate software application to create capability studies. And whatever you create can be shared with anyone who has Excel!

QI Macros is compatible with Excel 2007, 2010, 2013, 2016, 2011/2016 (Mac)

### QI Macros Tools that Perform Process Capability Analysis

**Histogram**- calculates Cp, Cpk, Pp, Ppk and twenty other metrics using your data and spec limits.**Capability Suite**- creates six charts including histogram, control charts, probability plot, values plot and capability plot. Also calculates Cp, Cpk and Pp, Ppk.**Cp Cpk Template**- calculates Cp, Cpk and Pp, Ppk on multiple sets of data.