Free quality planning tool
Target Cpk Calculator
See how much variation must be reduced—or how closely the process must be centered—to reach a required Cpk.
Planning support only. Confirm capability with a representative study, stable process, and suitable measurement system.
Calculate required improvementHow to use a target Cpk calculator
Cpk depends on both process centering and short-term variation. Enter your two specification limits, current mean and within-process sigma, then choose the required Cpk. The plan compares reducing variation at the current mean with moving the mean at the current variation.
How much variation reduction is needed for Cpk 1.33?
There is no universal percentage. The allowable sigma is the distance from the mean to the nearest specification divided by three times the target Cpk. A wider specification or a mean farther from the nearest limit permits more variation.
Can centering alone improve Cpk?
At the current sigma, the acceptable mean range is LSL + 3 × sigma × target Cpk through USL − 3 × sigma × target Cpk. If that interval exists, moving the mean into it can reach the target. If its lower bound exceeds its upper bound, variation must be reduced first.
Target Cpk Calculator FAQ
What Cpk should I target?
Use the requirement agreed with your customer or defined in the applicable quality plan. A value such as 1.33 is a planning example, not a universal acceptance requirement.
Can I improve Cpk by adjusting the process mean?
Yes, if the current within-process variation allows a feasible mean range. Moving the mean away from the nearest specification limit can improve Cpk without reducing sigma. If the range is empty, reduce variation first.
Does this calculator prove my process is capable?
No. It is a planning model based on supplied summary values. It does not establish normality, stability, measurement-system suitability or customer acceptance.
What is the difference between this planner and a full capability study?
This planner calculates improvement requirements from a mean and within-process sigma. A full study uses representative measurements to evaluate capability and performance, including Cp, Cpk, Pp and Ppk, with appropriate engineering checks.