Process Capability Calculator | Industrial Engineering Calculators

Process Capability Analysis

Process capability indices measure how well a process meets specifications. They compare the spread of the process variation to the width of the specification limits.

Cp = (USL - LSL) / (6σ) Cpk = min[(USL - μ) / (3σ), (μ - LSL) / (3σ)]
Pp = (USL - LSL) / (6s) Ppk = min[(USL - μ) / (3s), (μ - LSL) / (3s)]

Where:

USL = Upper Specification Limit
LSL = Lower Specification Limit
μ = Process mean
σ = Within-subgroup standard deviation (estimates short-term variation)
s = Overall standard deviation (estimates long-term variation)

Data Entry Method

Select how you want to enter your process data:

Summary Statistics

Individual Values

Subgroup Data

Enter Summary Statistics

Calculate capability indices using pre-calculated statistics.

Upper Specification Limit (USL):

Lower Specification Limit (LSL):

Process Mean (μ):

Within Subgroup Std Dev (σ):

Overall Std Dev (s):

Sample Size (n):

Enter Individual Values

Calculate capability indices from raw measurement data.

Upper Specification Limit (USL):

Lower Specification Limit (LSL):

Enter measurements (comma or space separated):

Subgroup Size (for within variation calculation):

Enter Subgroup Data

Calculate capability indices from subgrouped data (e.g., for control charts).

Upper Specification Limit (USL):

Lower Specification Limit (LSL):

Subgroup Size:

Enter subgroup data (one subgroup per line, values comma separated):

Process Capability Results

Cp

Potential Capability

Cpk

Actual Capability

Pp

Overall Potential

Ppk

Overall Performance

Sigma Level

Process Sigma

Process Statistics

Statistic	Value
Mean (μ)
Within Subgroup Std Dev (σ)
Overall Std Dev (s)
Sample Size (n)

Capability Interpretation

Index	Value	Interpretation
Cp
Cpk
Pp
Ppk

Estimated Defect Rates

Defect Type	Estimated Rate	Defects Per Million (DPMO)
Below LSL
Above USL
Total

Practical Examples

Example 1: Excellent Capability

USL = 10.5, LSL = 9.5, μ = 10.0, σ = 0.1, s = 0.12

Cp = 1.67, Cpk = 1.67, Pp = 1.39, Ppk = 1.39

This process is excellent with very low defect rates.

Example 2: Marginal Capability

USL = 10.5, LSL = 9.5, μ = 10.2, σ = 0.15, s = 0.18

Cp = 1.11, Cpk = 0.89, Pp = 0.93, Ppk = 0.74

This process is marginal and may produce some defects.

Example 3: Poor Capability

USL = 10.5, LSL = 9.5, μ = 10.3, σ = 0.25, s = 0.28

Cp = 0.67, Cpk = 0.44, Pp = 0.60, Ppk = 0.39

This process is not capable and needs improvement.

Process Capability Guidelines

Capability Index	< 1.0	1.0 - 1.33	1.33 - 1.67	> 1.67
Cp, Pp	Not capable	Marginal	Capable	Excellent
Cpk, Ppk	Not capable	Marginal	Capable	Excellent

Six Sigma Quality Levels

Sigma Level	Defects Per Million (DPMO)	Cpk Equivalent
1σ	691,462	0.33
2σ	308,538	0.67
3σ	66,807	1.00
4σ	6,210	1.33
5σ	233	1.67
6σ	3.4	2.00