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Cpk Calculator
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Process capability index measures the ability of a process to create product within specification limits. The value of Cpk is an index which measures how close a process is running to its specification limits, maintaining the natural variability of the process.

Therefore, process capability is defined based on the Cpk value as

Cpk = min ($\frac{USI-mean}{3 \times std.Deviation}, \frac{mean-LSL}{3 \times std.Deviation}$)
If
  • Cpk < 1, process is referred to an incapable of producing the product within specifications and
  • Cpk $\geq$ 1, process is referred to as capable of producing the product within specifications.
 

Steps for Cpk Calculator

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Step 1 :  

Read the problem and list out the values given.



Step 2 :  

Substitute the values in the corresponding formula.


Cpk = min ($\frac{USI-mean}{3 \times std.Deviation}, \frac{mean-LSL}{3 \times std.Deviation}$)



Problems on Cpk Calculator

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  1. Process improvement takes place and the USL value is 25 and LSL value is 15 and the mean value is 18. Calculate the Cpk value?


    Step 1 :  

    Given data


    USL = 25


    LSL = 15


    Mean value = 20



    Step 2 :  

    Substitute the alues in the corresponding formula.


    Cpk = min ($\frac{USI-mean}{3 \times std.Deviation}, \frac{mean-LSL}{3 \times std.Deviation}$)


    Cpk = min ($\frac{25-20}{3 \times 1}, \frac{20-18}{3 \times 1}$)


    Cpk = 0.667



    Answer  :  

    The answer is Cpk = 0.667



  2. A process possesses an average of 20 with a process width of 20. The USL is 25 and the LSL is 15. Calculate the Cpk value?


    Step 1 :  

    Given data


    USL = 25


    LSL = 15


    Mean value = 20



    Step 2 :  

    Substitue all the values in the formula


    Cpk = min ($\frac{USI-mean}{3 \times std.Deviation}, \frac{mean-LSL}{3 \times std.Deviation}$)


    Cpk = min ($\frac{25-20}{3 \times 10}, \frac{20-15}{3 \times 10}$)


    Cpk = 0.167



    Answer  :  

    The answer is Cpk = 0.167



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