User-entered process statistics

Process capability Cp/Cpk

Inputs

Lower specification limitLSLunitUser-entered lower requirement limit on the measured characteristic.

Upper specification limitUSLunitUser-entered upper requirement limit on the same characteristic.

Process meanx̄unitEstablished process mean on the same measurement basis.

Within-process standard deviationsunitUser-entered within-process standard deviation; establish its suitability separately.

Potential capability Cp

1.3333

—

Centered capability Cpk

1.0667

—

Upper capability Cpu

1.0667

—

Lower capability Cpl

1.6

—

Cp = (USL−LSL)/(6s); Cpk = min[(USL−x̄)/(3s), (x̄−LSL)/(3s)]

A first-pass number, not a code check, certification, or approval. Read the method and its limits below. What this is and is not.

Calculation snapshot

Formula version 1.0.0

Lower specification limit	9.80
Upper specification limit	10.20
Process mean	10.04
Within-process standard deviation	0.05

Cp = (USL−LSL)/(6s) · Cpk = min[(USL−x̄)/(3s), (x̄−LSL)/(3s)]

NIST process-capability reference: https://www.itl.nist.gov/div898/handbook/ppc/section4/ppc46.htm

This printout is a record of displayed inputs and deterministic formula output. It is not an approval, certification, or engineering conclusion.

Method

Calculate Cp, Cpk, and specification-side margins from limits, process mean, and within-process standard deviation.

Cp = (USL−LSL)/(6s); Cpk = min[(USL−x̄)/(3s), (x̄−LSL)/(3s)]

When

Don’t

Cp and Cpk compare user-entered specifications with user-entered process statistics. This screen does not establish statistical control, distribution suitability, rational subgrouping, measurement-system adequacy, sampling validity, customer requirements, capability thresholds, or production acceptance.