Cpk Calculator
Cpk is a number that shows how well a process stays inside its limits, and whether the average sits near the middle of them. Enter the average and spread of your measurements, and the two limits the product must meet.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
Cp compares the width of the allowed range with six standard deviations: the upper limit minus the lower limit, divided by six times the standard deviation. It ignores where the average sits.
Cpk uses the smaller of two distances: the upper limit minus the average, and the average minus the lower limit, each divided by three standard deviations. If the average is off-centre, Cpk is lower than Cp.
Worked example
With this average and spread, Cp is 2 and Cpk is 1.87.
Questions
Where do the average and spread come from?
Take a sample of measurements from the process, then work out their average and standard deviation. A standard deviation calculator can do the second step.
Should Cp and Cpk match?
Only when the average sits exactly in the middle of the limits. Otherwise Cpk is lower than Cp, which shows the process is off-centre.
Can this replace a quality engineer?
No. What the numbers mean depends on how the data was collected. Check the method with the people who run your quality system.
More like this
- Sales Tax CalculatorAdd sales tax to a price, or take it out of a total.
- Net Promoter Score CalculatorPromoter share minus detractor share, from survey counts.
- Markup CalculatorMarkup and margin from cost and selling price.
- Lead Time CalculatorExpected arrival from order date, production and shipping days.
- ROI CalculatorSimple and yearly return on an investment.
- Commission CalculatorCommission from sales, at one flat rate or two rates.