QM Bench

Capability Summary for Multiple Characteristics (Cpk Table)

Paste or import a table with one column per characteristic, LSL and USL rows and the measurements below. You get Cp, Cpk, Pp, Ppk, PPM, normality and stability for every characteristic at once.How to use ↓
  1. 1Enter your data
  2. 2Read the verdict
  3. 3Download the PDF report

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Paste one column per characteristic with LSL and USL rows, or import the sheet from Excel (keep the header row).

Table layout

The first row holds the characteristic names. Rows labelled LSL, USL and optionally Target give the specification. All other rows are measurements, in the order they were taken. This is the layout most inspection spreadsheets already use, so you can import the sheet directly from Excel.

Reading the summary

  • Capable: Cpk and Ppk both meet the required value and the process is stable.
  • Marginal: Cpk meets the requirement but Ppk does not, the process drifts between subgroups.
  • Not stable: special causes on the control chart, investigate before reporting a Cpk.
  • Not capable: Cpk below the requirement.

For any characteristic that needs a closer look, paste its column into the process capability study to see the control charts, histogram and distribution fit.

Frequently asked questions

›What is a capability summary used for?

For PPAP, a first article inspection or a process audit you usually need Cpk and Ppk for every characteristic on the drawing. The summary shows them in one table and highlights the characteristics that do not meet the requirement.

›How do I enter one-sided characteristics?

Leave the LSL or USL cell empty for that column. Runout, flatness or roughness usually only have an upper limit, and the tool then calculates Cpk from the existing limit only.

›Which subgroup size should I use?

Use the size of the rational subgroups in which the parts were taken, typically 5 consecutive parts. If every value comes from a different time, use subgroup size 1 so within sigma is estimated from the moving range.

›Why is a characteristic marked not stable?

At least one point is outside the control limits or a run rule was triggered. Open that characteristic in the process capability study to see the control chart before trusting the indices.