Cp Cpk Template for Excel
You Don't Have to be a Statistician to Analyze Capability using Cp and Cpk
What's Cool about the QI Macros Cp Cpk Template for Excel?
Just enter your target value, tolerances and measurements in the yellow shaded areas. The worksheet will automatically calculate Cp, Cpk, Pp, and Ppk. It has space for up to eight characteristics and 100 measurements:
Here is an Example of the QI Macros Cp Cpk Template
One Sided Spec Limits
If you need to perform a one tailed capability analysis, just delete the formula in either the USL or LSL field.
Cp and Cpk Calculation Mistakes to Avoid
Most people try to calculate Cp as the upper spec limit minus the lower spec limit divided by six times the standard deviation:
Cp = (USL-LSL)/6*Stdev
However, this is actually the formula for process performance (Pp).
The QI Macros Cp Cpk template uses the correct formula which estimates the standard deviation from the average of the ranges divided by a constant (Rbar/d2).
Cp = (USL-LSL)/6*Rbar/d2
The same is true for Cpk.
To open the template from the QI Macros menu, select SPC Charts, then Cp Cpk Worksheet about 2/3 down the list
To expand the template, follow these instructions (Click Here).
Learn More ...
- Process Capability Analysis Quick Reference Card (PDF, 172 KB)