What does the process capability ratio (Cp) compare?

The process capability ratio (Cp) is a statistical measure that compares the capability of a process to the specifications or tolerances set for that process. Specifically, it evaluates how well a process can produce outputs that meet predefined specifications without defects.

When determining Cp, the focus is on the range of acceptable variation in a process, which is defined by the upper and lower specification limits, against the actual variation of the process itself. A higher Cp value indicates a more capable process, where the spread of process variation is well within the specification limits, suggesting a high likelihood of producing quality outputs.

This comparison is critical in manufacturing and quality control, as it directly informs businesses about their operational efficiencies and areas where improvements might be needed to minimize rework or defects. Understanding this relationship helps organizations maintain quality standards and drive continuous improvement in their processes.