Process Capability Ratio Calculator

The process capability ratio, also known as the process capability index is statistical measurement of the ability of the process to produce desired output within a specified time period or other specified limits. It can also be termed as Cp and Cpk. The process capability index is helpful in planning process improvement measures. In the below Process Capability Ratio Calculator enter a data set, lower limit and upper limit and click calculate.

Process Capability Index (Cp and Cpk) Calculation

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x = (Mean - Lower Limit)/(3 x Standard Deviation) y = (Upper Limit - Mean)/(3 x Standard Deviation) Process Capability Ratio = min (x,y) Where, x = Process Capability Lower Limit y = Process Capability Upper Limit


A data set of values : 1,8,3,6,10 has lower limit as 2 and upper limit as 4.


From the data set, we can calculate
Standard deviation as 3.64692 and mean as 5.6
x = (5.6 - 2) / (3 x 3.64692)
= 0.329
y = (4 - 5.6) / (3 x 3.64692)
= -0.1462
Hence, Cp and Cpk index - 0.1462

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