The Difference Between 3 Sigma & 6 Sigma

The goal of a three sigma quality program is a deviation from an engineering specification of no more than one-sixth part — 1.66 percent, plus or minus. The goal of a Six Sigma quality program is a deviation of no more than one-twelfth part, or 0.83 percent, plus or minus. This represents a reduction in errors at every stage of the production process. While both three sigma and Six Sigma are used as measures of quality in a manufacturing environment, the difference is great. Three sigma represents a deviation from the engineering standard of 2,700 parts per million, versus two parts per billion for Six Sigma.