Six Sigma Calculator
Calculate your process capability and defect rate using Six Sigma methodology.
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Table of Contents
Six Sigma Formula
Six Sigma is a set of techniques and tools for process improvement. The sigma level indicates how many standard deviations fit between the process mean and the nearest specification limit.
How to Calculate Process Capability
To calculate the sigma level of your process, follow these steps:
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1Determine the upper and lower specification limits (USL and LSL)
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2Calculate the process mean (μ)
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3Calculate the standard deviation (σ)
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4Calculate the sigma level using the formula
Interpreting Sigma Levels
The sigma level indicates the process capability and defect rate. Here's how to interpret different sigma levels:
- 6σ: World-class performance, 3.4 defects per million opportunities.
- 5σ: Excellent performance, 233 defects per million opportunities.
- 4σ: Good performance, 6,210 defects per million opportunities.
- 3σ: Average performance, 66,807 defects per million opportunities.
- 2σ: Below average performance, 308,537 defects per million opportunities.
- 1σ: Poor performance, 691,462 defects per million opportunities.
Six Sigma - Practical Examples
Example 1 High-Performing Process
A process with USL = 10, LSL = 5, mean = 7.5, and standard deviation = 0.5.
Sigma Level = min((10 - 7.5) / 0.5, (7.5 - 5) / 0.5) = min(5, 5) = 5σ
Example 2 Average-Performing Process
A process with USL = 10, LSL = 5, mean = 7.5, and standard deviation = 1.0.
Sigma Level = min((10 - 7.5) / 1.0, (7.5 - 5) / 1.0) = min(2.5, 2.5) = 2.5σ
Example 3 Poor-Performing Process
A process with USL = 10, LSL = 5, mean = 7.5, and standard deviation = 2.0.
Sigma Level = min((10 - 7.5) / 2.0, (7.5 - 5) / 2.0) = min(1.25, 1.25) = 1.25σ