Capability Index Calculator

Formula

The formula to calculate the Capability Index (Cp) is:

\[ \text{Cp} = \frac{\text{USL} - \text{LSL}}{6 \times \sigma} \]

Where:

\(\text{Cp}\) is the Capability Index
\(\text{USL}\) is the Upper Specification Limit
\(\text{LSL}\) is the Lower Specification Limit
\(\sigma\) is the Standard Deviation of the Process

What is a Capability Index?

A Capability Index (Cp) is a statistical measure used in process management to assess the ability of a given process to meet specified requirements or specifications. It quantifies the alignment of the process output with the target, and the variability of the output. Common capability indices include Cp, Cpk, Pp, and Ppk, each providing different insights into process performance. A higher capability index indicates a more capable process, with less variability and fewer defects.

Example Calculation

Let's consider an example:

Upper Specification Limit (USL): 10
Lower Specification Limit (LSL): 2
Standard Deviation (σ): 1

Using the formula to calculate the Capability Index:

\[ \text{Cp} = \frac{10 - 2}{6 \times 1} = \frac{8}{6} \approx 1.33 \]

This means that the Capability Index (Cp) is approximately 1.33.