Enter the upper specification limit, lower specification limit, standard deviation, and process mean into the calculator. The CPK calculator will evaluate and display the process capability index of those values.

CPK Formula

The following formula is used to calculate the CPK, or process capability index, of a given set of data.

CPK = Min [(USL – mean/3 * std.),(mean-LSL/3*std.)]

  • Where CPK is the process capability index
  • USL is the upper limit
  • LSL is the lower limit
  • std is the standard deviation

CPK Definition

CPK is defined as the process capability index and is a measure of the ability of a process to produce objects to a customer’s specifications.

CPK Example

How to calculate CPK?

  1. First, determine the upper and lower limits.

    These are the upper and lower limits of the specifications.

  2. Next, determine the mean of the data.

    This is will be the average of all data points.

  3. Next, determine the standard deviation.

    This should be the standard deviation of the sample set.

  4. Finally, calculate the CPK

    Calculate the process capability index using the information from above and the equation.


What is CPK?

CPK is a term that standards for process capability index. The process capability index is a value used to measure the ability of a process to produce to a customer’s specifications.

How do you improve CPK?

Improve CPK by moving the upper and lower limits closer to the mean.

cpk calculator
cpk formula