Calculator Inputs
Example Data Table
| Cause | Defects | Severity | Occurrence | Detection | Cost/defect |
|---|---|---|---|---|---|
| Surface scratch | 42 | 6 | 7 | 5 | 120 |
| Loose fastener | 26 | 7 | 5 | 4 | 150 |
| Wrong label applied | 19 | 5 | 4 | 6 | 80 |
| Contamination | 12 | 8 | 3 | 6 | 200 |
| Tool wear | 15 | 5 | 6 | 4 | 90 |
Formula Used
- Share % (Pareto): Shareᵢ = (Defectsᵢ / Total Defects) × 100
- Cumulative %: sum of shares after sorting by defect count (descending).
- Risk Priority Number (RPN): RPNᵢ = Severity × Occurrence × Detection
- Cost impact: Costᵢ = Defectsᵢ × Cost Per Defectᵢ
- Composite score (0–100): each metric is normalized to 0–100 and blended: Scoreᵢ = wS·Shareᵢ + wR·(RPNᵢ/maxRPN·100) + wC·(Costᵢ/maxCost·100)
How to Use This Calculator
- Enter each defect cause and the number of defects observed.
- Rate Severity, Occurrence, and Detection from 1 to 10.
- Enter cost per defect (or use the default cost).
- Set your vital few threshold and weights for ranking.
- Click Calculate to see ranked causes and download outputs.
Why Defect Cause Ranking Matters
Defect cause ranking converts scattered inspection notes into a clear improvement queue. By combining frequency, risk, and cost, teams stop debating opinions and start acting on evidence. A ranked list also supports daily management: leaders can assign owners, set due dates, and track closure. When the same causes recur, the tool highlights systemic issues such as setup drift, operator method variation, or weak incoming control. This improves yield, delivery, and customer trust.
Collecting Comparable Input Data
Start with consistent definitions so each row represents one actionable cause, not a symptom. Record defect counts from the same time window, line, and inspection rule. If sampling varies, convert to defects per 1,000 units to keep comparisons fair. Use the 1–10 scales for Severity, Occurrence, and Detection with written anchors, for example 10 means safety or shutdown, while 1 is negligible. Consistency makes trends dependable. Review ratings monthly to prevent drift.
Pareto Share and Vital Few
Pareto share shows how much each cause contributes to total defects after sorting by count. Cumulative percentage reveals the “vital few” that typically drive most losses. A common starting point is 80%, but the threshold can be set to 70% for quick wins or 90% for deeper stabilization. Because cumulative share is additive, one fast‑growing cause will move into the vital few quickly, signaling urgency even before risk scoring changes. for leaders.
RPN and Cost Signals
Risk Priority Number (RPN) multiplies Severity, Occurrence, and Detection, creating a 1–1,000 signal that rewards prevention and early detection. Two causes with similar counts can have very different RPN values if one is hard to detect or has high customer impact. Cost impact adds a financial lens: rework, scrap, warranty, or downtime per defect multiplied by defects observed. Use cost when available, and keep assumptions documented for auditability. Strengthens funding decisions quickly.
Turning Scores into Actions
The composite score normalizes Share, RPN, and Cost to a 0–100 range, then blends them using your weights. If your site is quality‑critical, increase the RPN weight; if margin pressure is high, increase cost weight. After calculation, treat the top causes as a mini project portfolio: confirm the mechanism, run containment, and choose root‑cause tools like 5‑Why or fishbone. Recalculate weekly to verify that actions reduce counts measurably and shift the ranking.
FAQs
What is a defect cause in this tool?
A defect cause is an actionable driver you can remove or control, such as worn tooling, incorrect torque, or mislabeling. A defect type is the observed symptom. Use causes when you want owners and countermeasures.
How should I set Severity, Occurrence, and Detection?
Use a shared rating guide. Severity reflects impact on safety, compliance, and the customer. Occurrence reflects how often the cause happens. Detection reflects how likely current controls will catch it before shipment. Keep ratings consistent across teams.
What if I do not know the cost per defect?
Enter a reasonable estimate, or use the default cost for all rows to keep comparisons consistent. You can also set the cost weight to zero and rank using Pareto share and RPN only until better cost data is available.
How do the weights affect the ranking?
Weights scale the importance of defect share, RPN, and cost after each is normalized to 0–100. Increasing one weight raises causes strong on that metric. The tool automatically normalizes weights so the total remains 1.
Why does the vital few threshold matter?
The threshold defines which causes fall inside the cumulative Pareto cutoff. A lower threshold focuses on quick wins; a higher threshold captures more systemic contributors. Review the cutoff when volumes shift or when a new product mix arrives.
Can I share results with my team?
Yes. Use the CSV export for spreadsheets and the PDF export for a clean report. Include your rating guide and the time window used, so recipients interpret the ranking correctly and can track changes over time.