Process Capability Index Calculator
Calculate Cp, Cpk, Cpm, and Cpkm indices for quality control
Process Parameters
Maximum acceptable value
Minimum acceptable value
Average value of the process
Process variability (must be positive)
Example Calculation
Soup Temperature Control Example
Specification: Soup temperature must be 64-80°C
Process mean: 72°C
Standard deviation: 1.5°C
Calculation Results
Cp: (80 - 64) / (6 × 1.5) = 16 / 9 = 1.778
CPU: (80 - 72) / (3 × 1.5) = 8 / 4.5 = 1.778
CPL: (72 - 64) / (3 × 1.5) = 8 / 4.5 = 1.778
Cpk: min(1.778, 1.778) = 1.778
Result: Excellent process capability (Cpk > 1.33)
Capability Interpretation
< 0.67 - Poor
Process is not capable
0.67-1.00 - Inadequate
Process needs improvement
1.00-1.33 - Adequate
Marginally capable
1.33-2.00 - Good
Process is capable
> 2.00 - Excellent
World-class (6-sigma)
Key Concepts
Cp: Potential capability assuming perfect centering
Cpk: Actual capability considering process centering
Cpm: Capability relative to target value
Cpk ≥ 1.33: Industry standard for capable process
Understanding Process Capability Index
What is Process Capability?
Process capability indices measure how well a process can produce output within specification limits. They compare the width of the process distribution to the width of the specification limits, helping determine if a process is capable of meeting customer requirements.
Types of Indices
- •Cp: Measures potential capability if process is perfectly centered
- •Cpk: Measures actual capability considering process centering
- •Cpm: Capability relative to a specific target value
- •Cpkm: Combined measure of centering and target deviation
Formula Explanations
Cp = (USL - LSL) / (6σ)
Cpk = min[(USL - μ)/(3σ), (μ - LSL)/(3σ)]
Cpm = Cp / √[1 + ((μ - T)/σ)²]
Cpkm = Cpk / √[1 + ((μ - T)/σ)²]
- USL: Upper Specification Limit
- LSL: Lower Specification Limit
- μ: Process Mean
- σ: Standard Deviation
- T: Target Value
Industry Standards & Applications
Manufacturing
Quality control in production processes, ensuring products meet dimensional and performance specifications.
Six Sigma
Cpk ≥ 2.0 indicates 6-sigma quality level with 3.4 defects per million opportunities (DPMO).
Service Industries
Service time, quality metrics, and customer satisfaction measurements in service processes.