| Cause | Occ. | Sev | Det |
|---|---|---|---|
| Misaligned fixture | 9 | 8 | 6 |
| Worn cutting tool | 7 | 7 | 5 |
| Operator training gap | 6 | 6 | 7 |
| Material variation | 4 | 5 | 6 |
| Measurement drift | 2 | 7 | 8 |
- Enter sample size and total defects for the inspection.
- Add each suspected cause and its observed occurrences.
- Set Severity and Detection from 1–10, consistently.
- Add cost and downtime estimates if available.
- Click Analyze Causes to rank priorities.
- Export CSV/PDF for reviews and corrective action tracking.
- Defect Rate (%) = (Total Defects ÷ Sample Size) × 100
- DPU = Total Defects ÷ Sample Size
- DPMO = DPU × 1,000,000 (assumes 1 opportunity per unit)
- Estimated Sigma = NORMSINV(Yield) + 1.5, where Yield = 1 − DPMO/1,000,000
- RPN = Severity × Occurrences × Detection
- Priority Score (0–100) = (0.60·RPNₙ + 0.25·Costₙ + 0.15·Downtimeₙ) × 100
Defect signal to actionable priority
Start with sample size and the total defect count. The calculator converts this into defect rate and DPMO, then estimates yield and sigma. Treat sigma as a directional benchmark for comparing runs, not a certification result. When defect rate is above target, move to the ranked cause list to avoid spreading effort across low impact items.
Cause occurrence distribution and Pareto focus
Occurrences compute share and cumulative share. Sort causes by occurrences and identify the smallest set that reaches about eighty percent cumulative impact. This provides a practical focus list for containment actions, trial fixes, and verification checks. If your top causes shift week to week, review definitions and whether inspectors are classifying consistently.
FMEA scoring inputs and RPN behavior
Each cause uses Severity, Detection, and Occurrence to form an RPN. Severity reflects customer or safety impact if the defect escapes. Detection reflects how likely current controls catch the issue before shipment. Occurrence is the observed frequency you entered. High severity with weak detection can outrank a frequent but low impact issue, which helps when risk matters more than volume.
Cost and downtime as business signals
Cost per event and downtime minutes add operational context. The calculator normalizes RPN, cost, and downtime, then blends them into a single priority score. Use cost for scrap, rework, warranty, or inspection labor. Use downtime for line stoppage, changeover, or troubleshooting. This blend helps leadership compare corrective actions across processes.
Interpreting the priority score responsibly
The priority score ranges from zero to one hundred within your dataset. It is relative, so it changes if you add or remove causes. Use it to decide what to validate first, then confirm with data such as gage R&R, capability, or controlled experiments. After improvements, re-enter updated values to show risk reduction and document control plan changes.
Turning analysis into a corrective action plan
Export results and assign owners for the top ranked causes. Add a containment step, a root cause validation method, a corrective action, and a verification metric such as defect rate, DPMO, or downtime. Track dates and evidence. When the Pareto bar drops and detection improves, lock the change with standard work, training, and audits. And repeat the review monthly.
What does the Pareto cutoff rank mean?
It is the first rank where cumulative occurrence reaches about 80%. Focus your initial containment and validation work on causes up to this rank to reduce defects quickly.
How should I choose Severity and Detection scores?
Use a consistent rubric. Severity should reflect customer, safety, and regulatory impact. Detection should reflect how likely current controls catch the issue before shipment; higher means harder to detect.
Why can a low-occurrence cause rank high?
RPN multiplies Severity, Occurrence, and Detection. A rare but severe issue with weak detection can legitimately outrank frequent low-impact issues when risk exposure matters.
Is the sigma value an official capability result?
No. It is a directional estimate derived from DPMO and an inverse normal approximation with a 1.5σ shift. Use it for comparison across runs, not for formal certification.
Can I use cost and downtime together?
Yes. Cost captures financial loss per event, while downtime captures operational disruption. Combining both helps prioritize fixes that improve quality and throughput simultaneously.
What should I do after implementing a fix?
Re-measure defects and update occurrences, detection, and costs. Re-run the analyzer to confirm the Pareto improves and the priority score drops, then document changes in the control plan.