Six Sigma is a statistical term used to measure the number of defects that processes create. A process performing at a Six Sigma level allows only 3.4 defects per one million opportunities. The higher the Sigma level, the better the quality of the product or service and the fewer the defects2. Here’s the relationship between Sigma levels and DPMO (Defects Per Million Opportunities):

1σ (One Sigma): DPMO = 691,462 (69.1% yield; 30.9% defect rate)

2σ (Two Sigma): DPMO = 308,538 (93.1% yield; 6.9% defect rate)

3σ (Three Sigma): DPMO = 66,807 (99.3% yield; 0.7% defect rate)

4σ (Four Sigma): DPMO = 6,210 (99.98% yield; 0.02% defect rate)

5σ (Five Sigma): DPMO = 233 (99.977% yield; 0.023% defect rate)

6σ (Six Sigma): DPMO = 3.4 (99.99966% yield; 0.00034% defect rate)1

Therefore, achieving Six Sigma performance means maintaining a defect rate of 3.4 defects per million opportunities1.