Capability Analysis in Excel

Capability analysis determines if a process will deliver a product that meets the customers specifications (USL/LSL) and how well it is centered between the specification limits.

Not Capable
Capable
Not Capable to Centered & Capable
Histogram NOT CAPABLE
Cp < 1, Cpk <1

Cp >= 1, Cpk >= 1

Cp and Cpk
Process Capability Indicies

  • Cp measures how well the data fits 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
Process Performance Indicies

  • Pp measures how well the data fits 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 Cpk Calculation Mistakes to Avoid

You can calculate Cp, Cpk and Pp Ppk manually or you can use the QI Macros for Excel. Based on calls to our tech support line, most people who try to perform manual calculations or build their own Excel formulas end up with incorrect results. For example, they use stdev instead of sigma estimator for Cp and Cpk. Or they get the constant wrong based on their sample size. If you're providing these results to your customers shouldn't you use a tool that's proven and affordable?

QI Macros Tools that Perform 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.

Learn More ...

Create these charts and diagrams yourself in just seconds using the QI Macros for Excel...
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