Cpk measures actual capability, factoring in both the variation and how well-centered the process is. Generally, organizations aim for Cp ≥ 1.33 and Cpk ≥ 1.33 as a minimum standard for capability. Some industries (e.g., aerospace or medical) may target 1.67 or higher.

A Cpk≥1.33 is desirable, a value of Cpk=0 implies that 50% of the process output falls beyond the specification limits. The larger the index, the less likely it is that any parameter will be outside the specification.

Cpk = or >1.33 indicates that the process is capable and meets specification limits. Any value less than this may mean variation is too wide compared to the specification or the process average is away from the target.

Table 1 shows some Cpk values and their equivalent ppm rates. In the semiconductor industry, the Cpk goal for a process is normally set at 1.67 , although a Cpk of 1.33 is still considered acceptable.

2025年3月14日 · A Cpk of 1.33 means the process is producing outputs that are within ±4σ (sigma) of the mean, leaving a defect rate of approximately 63 parts per million (ppm). In summary, a Cpk of 1.33 is the threshold for a “capable and reliable process” in most industries, ensuring both efficiency and quality without excessive costs.

A Cpk value less than 1.0 is considered poor and the process is not capable. A value between 1.0 and 1.33 is considered barely capable, and a value greater than 1.33 is considered capable. But, you should aim for a Cpk value of 2.00 or higher where possible.

Process capability indices measure how much "natural variation" a process experiences relative to its specification limits, and allows different processes to be compared to how well an organization controls them. Somewhat counterintuitively, higher index values indicate better performance, with zero indicating high deviation.

In a quality control context, PPM stands for the number of parts per million (cf. percent) that lie outside the tolerance limits. Cpk 1.00 means that 2 700 PPM (0.27%) of the manufactured parts are out of tolerance, while Cpk 1.33 means that 63 PPM (0.0063%) are rejects.

2023年6月22日 · A CPK or PPK value of 1.33 indicates that the process is capable and performing well, with room for some process shifting or changes in short-term variation. A CPK or PPK value greater than 1.67 suggests the process is performing excellently, with enough margin to accommodate shifts or changes in short-term variation.

This calculator helps you determine a process’s capability indices (Cp and Cpk) based on your specified limits, mean, and standard deviation. Enter the upper and lower specification limits (USL, LSL). Enter the process standard deviation (σ) and mean (μ). Click Calculate to see Cp and Cpk, along with feedback on process capability.