Quality & Metrology worked example
Pp with tolerance width of 0.15 spec units: a worked example
Suppose tolerance width falls to 0.15 spec units. This page works the full calculation at that level so you can see exactly which result moves and by how much. Estimate process performance Pp by comparing the tolerance width to the long-term process spread for a feature.
The inputs for this scenario
- Tolerance width (USL minus LSL): 0.15 spec units (the input this scenario stresses; the baseline uses 0.3)
- Long-term process spread (6 sigma): 0.27 spec units (held at the documented default)
- Reporting conversion factor: 1 x (held at the documented default)
Working through the calculation
- The calculation starts from the formula this tool documents: Pp = tolerance width รท long-term process spread.
- Process performance Pp works out to 0.56 Pp at these inputs, and this is the headline figure for the scenario.
- Raw ratio works out to 0.56 value at these inputs.
- Conversion factor works out to 1 x at these inputs.
- Long-term process spread (6 sigma) works out to 0.27 value at these inputs.
How this compares with the baseline
- Against the tool's baseline example, where tolerance width sits at 0.3 spec units and the headline result is 1.11 Pp, this scenario comes in 50% below the baseline at 0.56 Pp.
- It divides the total specification tolerance width by the long-term six-sigma process spread to produce the Pp performance ratio. When the numbers land here, the stressed input is the lever to work; the walkthrough above shows exactly how much each output recovers as it climbs back toward the baseline.
Results at a glance
- Process performance Pp: 0.56 Pp (headline result)
- Raw ratio: 0.56 value
- Conversion factor: 1 x
- Long-term process spread (6 sigma): 0.27 value
Run it with your numbers
- To rerun this with your own numbers, open the live Pp calculator, set tolerance width to your actual value, and adjust the remaining inputs to match your operation.
Last reviewed 2026-05-12.