Process capability tool
v2.2|Updated May 2, 2026
Cp, Cpk, Pp and Ppk Calculator
Calculate capability and performance indices from pasted measurements or summary statistics. Use the planner to estimate centered specification limits for a target index.
Cp/Cpk usually use within-process variation. Pp/Ppk use overall variation. With one pasted dataset, results may match unless different standard deviation estimates are entered.
Step 1
Paste measurement data
Separate values with commas, spaces, tabs, or new lines.
Step 2
Specification limits
Enter the engineering limits used to judge the process.
Statistics
Basic study results
Use within-process or short-term standard deviation.
Enter data to see the basic statistics.
Capability
Cp / Cpk results
Cpk is controlled by the weaker side of the process.
Enter data first.
Plot
Data sequence and distribution
First review the measurements in order, then compare the overall distribution shape.
Paste raw data to see the chart.
Learning center
Process capability guides
Use the calculator, then read the guide that matches the question you are trying to answer.
What is Cpk?
Understand Cpk, CPU, CPL, and capability risk.
Cp vs Cpk
Learn potential capability versus actual capability.
Pp vs Ppk
Compare performance indices with capability indices.
Histogram bins
See how bin rules affect distribution charts.
Sample size
Why small samples can make Cpk unstable.
Methodology
Review formulas, assumptions, and limitations.
Interactive guide
Learn the terms visually
Click a term to see what changes in the process picture.
If the mean moves left or right, the process center moves with it.
Mean
Mean is the process center
Mean is the average of all measurements. It tells you where the process is centered and whether the process is drifting toward the upper or lower specification limit.
Cp vs Cpk: potential vs actual
Cp asks whether the process spread can fit inside the specification limits if it is centered. Cpk asks where that same spread actually sits. When the mean shifts toward USL or LSL, part of the curve can move beyond the limit, so Cpk drops even when Cp still looks good.
Cp vs Cpk visual example
Same spread, different centering.
Cp view: centered process
Cp describes potential capability by comparing spread with the tolerance band. When the curve is centered, Cpk can match Cp.
Cpk view: same spread, shifted mean
The spread is unchanged, so Cp stays high. Cpk falls because the shifted curve now extends beyond the upper specification limit.