FMEA RPN and Risk Reduction Calculator
RPN is still used in many plants and supplier forms. This calculator multiplies severity, occurrence and detection before and after an action so you can show the impact and see how detection ratings affect the result.
Your numbers
1 to 10 per your severity scale.
Higher means harder to detect.
Use your own rule, if you still use RPN thresholds.
Your results
RPN is a legacy ranking aid. The AIAG-VDA FMEA handbook uses Action Priority, which weights severity first, so check your own AP table and customer requirements before deciding on action.
RPN after vs detection rating
Sweeps Detection after from 1 to 10, holding your other inputs fixed.
Compare FMEA ratings with ERP quality data
Optional: we can check whether your occurrence ratings match actual scrap and NCR history.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the current severity, occurrence and detection from your FMEA row. Then enter the ratings you expect after the action, or the verified ratings after implementation. The calculator returns both RPNs, the reduction and a percentage. Use the chart to see how much the result depends on detection, then decide whether a prevention action would be stronger.
- Ratings are 1 to 10
- Higher detection rating means harder to detect
- Keep severity constant unless the effect changes
- Use verified values after implementation
The formula
Risk Priority Number equals severity times occurrence times detection, so the range is 1 to 1000. For example, 8 x 5 x 6 gives 240. After an action that cuts occurrence to 3 and detection to 4, the RPN is 8 x 3 x 4, or 96, a reduction of 144 or 60 percent. The same product can come from very different combinations, which is a known weakness.
Why Action Priority replaced RPN
Equal RPNs can hide very different risk. A severity 10 item with occurrence 2 and detection 2 has an RPN of 40 but may be unacceptable. The AIAG-VDA method assigns high, medium or low Action Priority from a table that looks at severity first, then occurrence, then detection. This calculator also reports severity times occurrence to help see that pattern.
Common mistakes
Do not use a detection improvement as the main fix when prevention is available. Do not re-score without verified evidence. Do not compare RPNs across different FMEAs that use different scales. And do not treat a single RPN threshold such as 100 as a universal rule; it was never a standard.
Frequently Asked Questions
What is a good RPN?
There is no universal value. Some teams used 100 as an action trigger, but the AIAG-VDA handbook discourages fixed thresholds. Look at severity first, then occurrence and detection, and follow your customer requirements.
Why does a high detection number mean worse?
On the standard scale, detection 1 means the control almost certainly detects the problem and 10 means it is not detected. So a lower detection rating after an action means a better control.
Can the RPN drop without real improvement?
Yes, if ratings are changed without evidence. Always tie new ratings to implemented and verified controls, such as a validated poka-yoke or a gauge study.
Does it work for DFMEA?
Yes for the arithmetic. DFMEA scales differ from PFMEA scales, so use the matching tables when choosing the ratings.
If you want FMEA ratings compared against real scrap and escape data from your ERP, Netray can help. Ask for a short review.
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