Process Capability Cp and Cpk Calculator
The process capability calculator estimates Cp and Cpk from a process mean, within-process standard deviation and upper/lower specification limits.
How to use this calculator
- Enter the observed process mean, a positive within-process standard deviation, and limits with USL greater than LSL.
- Check the units and definitions before comparing results with another source.
- Change one input at a time when comparing scenarios, and keep the reporting period and assumptions consistent.
Formula used by the process capability cpk calculator
Cp = (USL − LSL)/(6σ); Cpk = min((USL − μ)/(3σ), (μ − LSL)/(3σ))
- Cp = (USL − LSL)/(6σ); Cpk = min((USL − μ)/(3σ), (μ − LSL)/(3σ))
- Capability indices should be interpreted only when the process is stable and the chosen standard deviation and specification limits are appropriate.
- Inputs are checked for required values and valid ranges; displayed results are rounded for readability.
Worked examples
Worked example
Mean 10, standard deviation 0.5, specification limits 8.5 and 11.5.
Cp = 1.0; the mean is centred, so Cpk is also 1.0.
Cp = 1.0; the mean is centred, so Cpk is also 1.0.
Understanding the result
The process capability calculator estimates Cp and Cpk from a process mean, within-process standard deviation and upper/lower specification limits.
Capability indices should be interpreted only when the process is stable and the chosen standard deviation and specification limits are appropriate.
Important notes
Capability indices should be interpreted only when the process is stable and the chosen standard deviation and specification limits are appropriate.
The result applies to the numbers and assumptions entered here; verify specifications for safety-critical or regulated uses.
Frequently asked questions
Why can Cpk be lower than Cp?
Cpk accounts for how close the process mean is to the nearest specification limit, while Cp considers width only.
Does a Cpk value prove product quality?
No. It is a statistical summary and should be interpreted with stability, sampling and specification context.
How do I use this calculator?
Enter the observed process mean, a positive within-process standard deviation, and limits with USL greater than LSL.
Affiliate recommendations
Tools related to Process Capability Cp and Cpk Calculator
These tools are selected for the calculator topic. The Calc Studio may earn a commission from purchases made through affiliate links.
- BusinessAnywhere business services Visit partner ↗
Business formation and business services for entrepreneurs and online businesses.
See the Affiliate Disclosure for details.
Related calculators
- X-Bar Control Chart Limits Calculator — Calculate three-sigma control limits for an X-bar chart from process variation and subgroup size.
- Full-Time Equivalent Calculator — Convert weekly workload hours into full-time equivalent staffing units using a chosen standard work week.
- Average Selling Price Calculator — Calculate net average selling price per unit from revenue and units sold over a matching period.
- Cost per Lead Calculator — Calculate campaign cost per lead from advertising spend and a consistent lead count.
- Current Ratio Calculator — Calculate the current ratio and working capital from current assets and current liabilities.
- Days Payable Outstanding Calculator — Estimate days payable outstanding from average accounts payable and cost of goods sold for a chosen period.
Related explanations
Learn the method behind the number or compare the terminology before using the calculator.
- How to Calculate a Z-Score — Learn how a z-score shows how far a value is from the mean in standard-deviation units.
- How to Calculate Salary from an Hourly Rate — Convert hourly pay into weekly, monthly, and annual estimates and understand the assumptions behind the result.
- Markup — Learn what markup means, how markup is calculated from cost and selling price, and how it differs from margin.
This page provides a calculation tool plus explanatory information so you can understand what the result means and when the underlying method may not fit your situation.