Cp focuses on potential capability
Cp asks whether process variation is narrow enough for the tolerance range if the process is perfectly centered. It is best understood as a measure of potential capability rather than actual performance.
Process Capability Guide
Cp vs Cpk
Cp and Cpk are closely related process capability metrics, but they answer different questions. Looking at both helps you avoid misreading a process that is statistically tight but operationally off-center.
Cpk includes centering and actual performance
Cpk asks whether the real process location and variation together can meet the specification limits. That makes Cpk more useful when you want to understand actual production risk.
How to interpret Cp vs Cpk together
If Cp is high and Cpk is low, the process may have enough potential capability but is likely off target. If both Cp and Cpk are low, excessive variation is usually the main issue. If both are high, the process is generally narrow and well-centered relative to the specification limits.
When engineers search for Cp vs Cpk
Teams often compare Cp vs Cpk when preparing customer reports, troubleshooting defects near a specification limit, or deciding whether a process needs centering adjustment or variation reduction.
A practical way to read Cp vs Cpk
A simple rule of thumb is this: if Cp and Cpk are both high, the process is narrow and centered. If Cp is high but Cpk is lower, centering is likely the issue. If both are low, the spread itself is the bigger concern. This kind of side-by-side interpretation is often more useful than focusing on one index by itself.
Process capability calculator
If you want to move from theory to practice, use the Cp / Cpk calculator to upload data, enter specification limits, and review capability metrics with a histogram and plain-language interpretation.
Try the calculator
Use the calculator on the main page to compare sample data, upload your own measurements, and see how Cp and Cpk change with different specification limits.
Open the calculatorFrequently asked questions
What is the main difference between Cp and Cpk?
Cp looks at process spread only, while Cpk includes both spread and centering relative to the specification limits.
Should Cp and Cpk be reviewed together?
Yes. Looking at both metrics helps you separate variation problems from centering problems.
What does it mean if Cp is high and Cpk is low?
That usually means the process has enough potential capability but is shifted away from the target center.