PPM calculations for 6 Sigma

#4
Ramkiran,

You first need to understand the difference between Cp and Cpk.

Cp (Capability of the process) only describes the variation of the process in respect to width of the specs, regardless if it is centered within specs.
Cpk(Cabibility of the process katayori {katayori is Japanese for centered}) describes both the variation and its ability to deliver results within your specs. Cp>= Cpk.

If you have a Cp of 1.0, that means that the spec width is 6 standard deviations across.

Cpk is more conservative and gives you the calaculation based on the minimum of the two distances from the center to specs.

With a little algebra you should be able to use this site to derive PPM: https://www.isixsigma.com/tools-tem...cp-cpk-pp-and-ppk-know-how-and-when-use-them/