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How to calculate the sigma level of a process and Relationship of DPMO

Hi there,

Now the six sigma is buzzword in many area. My question is how to calculate process sigma level.

For exmaple, suppose there is no shift in process, our process means is 100, taget is also 100,process sigma(by R/d2 calculating) is 1.8, specification is 90–110,

Question1: how to calculate sigma level?
is it (110-90)/6*1.8?
Question2: now I am also confusing how to calculate the cpk of this ?


The calculation of a Sigma level, is based on the number of defects per million opportunities (DPMO).

In order to calculate the DPMO, three distinct pieces of information are required:
a) the number of units produced
b) the number of defect opportunities per unit
c) the number of defects

The actual formula is:

DPMO = (Number of Defects X 1,000,000)

((Number of Defect Opportunities/Unit) x Number of Units)


A manufacturer of computer hard drives wants to measure their Six Sigma level.
Over a given period of time, the manufacturer creates 83,934 hard drives.
The manufacturer performs 8 individual checks to test quality of the drives.
During testing 3,432 are rejected.

Defects 3432 DPMO 5111.158768
Opportunities 83934 Sigma Level 4.1
Defect Opportunities per unit 8

Six Sigma Table: 1 690,000
2 308,000
3 66,800
4 6,210
5 320
6 3.4