Process capability is the long-term performance level of the process after it has been brought under statistical control. In other words, process capability is the range over which the natural variation of the process occurs as determined by the system of common causes. .

• Process capability is also the ability of the combination of people, machine, methods, material, and measurements to produce a product that will consistently meet the design requirements or customer expectation.
• Process capability study is a scientific and a systematic procedure that uses control charts to detect and eliminate the unnatural causes of variation until a state of statistical control is reached.
• When the study is completed, you will identify the natural variability of the process.
• Cp, Cpl, Cpu, and Cpk are the four most common and timed tested measures of process capability.
• Process capability indices measure the degree to which your process produces output that meets the customer's specification.
• Process capability indices can be used effectively to summarize process capability information in a convenient unitless system.
• Cp and Cpk are quantitative expressions that personify the variability of your process (its natural limits) relative to its specification limits (customer requirements).