# How to Calculate Process Capability Index

A Simple short tutorial on how to find process capability index with step by step example calculation.

## How to Calculate Cpk

Process Capability Index (C_{pk}) is the statistical measure of process capability. It is also called as Process Capability Ratio. It is the ability of a process to generate output in the state of statistical control. There are two types of data being analyzed using the concept of process capability, they are continuous data an variable data. The solution of the index is usually expressed as calculations or histograms. Use our online short tutorial to learn how to calculate Process Capability Index in simple step process.

**Process Capability Index Formula: **

Learn here how to calculate Cpk using the process capability ratio formula.

C_{pk }= (USL - Mean / 3.S ) , (Mean - LSL / 3.S)

**where**,

USL = Upper Specification Limit

LSL = Lower Specification Limit

S = Standard Deviation

**Example**

**Step 1:** Consider that in an Ice cream parlour, the ideal serving temperature range is between **4°F** and **10°F**. The freezer that is used to maintain the ideal temperature has a process standard deviation of **2°F **and the mean value for these temperature is 8. Find the Process Capability Index ?

Given,

USL (Upper Specification Limit) = **10°F**

LSL (Lower Specification Limit) = **4°F**

Standard Deviation =**2°F**

Mean = 8

**Step 2:** Substitute the given values in the formula

C_{pk }= (USL - Mean / 3.S ) , (Mean - LSL / 3.S)

**Find (USL - Mean / 3.S ),**

= (10 - 8 / 3 x 2)

= (2/6) = 0.3

**Find ****(Mean - LSL / 3.S)**

= (8 - 4 / 3 x 2)

= (4 / 6) = 0.6

The minimum value obtained is the process capability Index value.

C_{pk }= (USL - Mean / 3.S ) , (Mean - LSL / 3.S)

= min (Solution 1, Solution 2)

= min ( 0.3, 0.6)

= 0.3

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