It is a methodology and set of tools for the measurement of process quality. It demonstrates that the business process is well controlled. Six Sigma level can be achieved when the accuracy of your process gets only 3.4 defects per million opportunities.

Here’s the list of acceptable number of defects per million to correspond to each Sigma level:

Sigma level Defects per million opportunities

1 690,000

2 308,537

3 66,807

4 6,210

5 233

6 3.4