1. What is Cpk?

The Process Capability Index (Cpk) measures how well a process can produce output within specification limits. It considers both the process variability and how centered the process is between the specification limits.

2. How Does the Calculator Work?

The calculator uses the Cpk formula:

Where:

• \( USL \) — Upper Specification Limit
• \( LSL \) — Lower Specification Limit
• \( \mu \) — Mean of the data
• \( \sigma \) — Standard deviation of the data

Explanation: Cpk is the minimum of two values representing how many standard deviations fit between the mean and each specification limit.

3. Importance of Cpk Calculation

Details: Cpk is crucial for quality control, process improvement, and ensuring products meet specifications. Higher Cpk values indicate better process capability.

4. Using the Calculator

Tips: Enter your data as comma-separated values, along with the upper and lower specification limits. The calculator will compute the mean, standard deviation, and Cpk.

5. Frequently Asked Questions (FAQ)

Q1: What is a good Cpk value?
A: Generally, Cpk ≥ 1.33 is considered capable, ≥ 1.67 is good, and ≥ 2.00 is excellent.

Q2: How is Cpk different from Cp?
A: Cp only considers process spread, while Cpk also considers how centered the process is between the limits.

Q3: What if my Cpk is negative?
A: A negative Cpk indicates the process mean is outside the specification limits.

Q4: How many data points are needed?
A: For reliable results, at least 25-30 data points are recommended.

Q5: Can Cpk be greater than Cp?
A: No, Cpk can never exceed Cp as it's the more restrictive measure.