What is the PPM (parts per million) for a 6 sigma level?

The PPM (parts per million) for a six sigma level is 3.4 ppm. This metric indicates the number of defects that are expected to occur per million opportunities when a process is operating at a six sigma level of performance.

In Six Sigma terminology, the "sigma level" refers to the capability of a process; a six sigma process is one that produces fewer than 3.4 defects per million opportunities. This is a benchmark that illustrates the effectiveness and quality of a process, demonstrating that it operates at a very high level of precision with minimal variation.

The significance of the 3.4 ppm rate stems from the statistical properties of a normal distribution, where the goal of six sigma is to ensure that the process mean is six standard deviations away from the nearest specification limit. This positioning creates a very small area under the curve that corresponds to defects, hence the low defect rate of 3.4 ppm.

In practical terms, achieving a six sigma level means that the process is extremely stable, reliable, and capable of consistently producing products or services that meet quality criteria. Thus, this quality benchmark is highly valued in industries that require rigorous quality control standards.