Control chart and process capability calculator
Paste measurements in time order and enter lower and upper specification limits. The tool builds an individuals chart from moving ranges and calculates Cp and Cpk.
Individuals control chart
The line shows measurements over time. Horizontal lines mark the mean, control limits and specification limits.
Measurements and signals
| No. | Measurement | Mean | LCL | UCL | Outside control (1 = yes) |
|---|---|---|---|---|---|
| Fill in the fields above — the result is computed on this page. | |||||
How to use this page
- Paste measurements in their true time order.
- Enter approved specification limits.
- Inspect chart stability before interpreting Cp and Cpk.
What this page does not do: The model uses an individuals chart and sigma ≈ average moving range / 1.128. It does not replace measurement-system, normality, autocorrelation or SPC plan reviews.
Further reading
Control limits describe observed process variation, while specification limits come from requirements. They are different concepts. Cp compares specification width with process spread; Cpk also accounts for mean centring.
Assess process stability first. Capability indices can mislead when special causes remain in the data.
Frequently asked questions
Are LSL and USL control limits?
No. Specifications come from requirements; control limits are estimated from process behaviour.
What Cpk is good?
The threshold depends on the industry, risk and agreement. A single index is insufficient without a stable process and reliable measurement system.
See also
A/B test calculator
Compare two proportions in an A/B test. Calculate conversion rates, difference, uplift, z score, p value and c
A/B test planning — sample size, MDE and duration
Plan a two-proportion experiment, estimate detectable effect and traffic duration.
ACF and PACF autocorrelation calculator
Calculate ACF and PACF across time-series lags. Review the chart, reference bounds and coefficient table.