Top

Cpk Calculator
Top
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

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

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

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