FMEA RPN Reduction What-If Calculator
The risk priority number is still the number most teams are asked to show on a recommended action line. This calculator takes the current ratings and the ratings you expect after the action, and shows what the action buys you.
Your numbers
Effect on the customer or next process. Severity normally does not change unless the design changes.
How often the cause is expected to occur today.
How well current controls detect the cause or failure before it reaches the customer.
Rating you expect once the prevention action is verified.
Rating you expect once the detection action is verified.
Your internal threshold. Many sites use 100 or 120 as a trigger, but there is no universal limit.
Your results
RPN is S x O x D on 1 to 10 scales. AIAG and VDA FMEA (2019) moved to Action Priority; use this for legacy RPN-based procedures and quick comparisons.
RPN after action vs planned detection rating
Sweeps Planned detection after action from 1 to 10, holding your other inputs fixed.
FMEA data from your ERP
Optional review of how nonconformance and inspection history in your ERP could feed FMEA occurrence and detection ratings.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the severity, current occurrence and current detection from your PFMEA or DFMEA row. Then enter the occurrence and detection you expect after the recommended action is implemented and verified. The calculator multiplies the three ratings, shows the percentage reduction and compares the result with your target. The chart sweeps the planned detection rating from 1 to 10 so you can see which level of control is worth pursuing.
- Keep severity fixed unless the design or effect changes.
- Prevention actions lower occurrence; inspection and test actions lower detection.
- Only enter post-action ratings you can justify with evidence.
The formula and its limits
RPN equals severity times occurrence times detection, giving a value from 1 to 1000. Because the ratings are ordinal, the product has well-known weaknesses: very different risk profiles can share the same RPN, and a severity 10 with low occurrence can score lower than a severity 4 with poor detection. This is why the 2019 AIAG and VDA handbook replaced RPN thresholds with Action Priority. Use RPN as a ranking aid, never as the only decision rule.
Reading the result
A large percentage drop from a detection-only action can look impressive but leaves the cause untouched; defects still occur and you rely on the inspection catching them. Compare a prevention action against a detection action using the same row. If the RPN is below target but severity is 9 or 10, the flag output reminds you that the item still needs a documented review.
Common mistakes
The most common error is entering hoped-for ratings before the action is proven. Another is lowering detection on a control that only works sometimes, such as visual inspection. Finally, teams often chase RPN thresholds by rating inflation. Update the post-action ratings only after the control plan reflects the change and data confirms it.
Frequently Asked Questions
What is a good RPN?
There is no universal good value. Sites set their own trigger, often 100 or 120, and also review any severity of 9 or 10. Compare to your own procedure rather than an outside number.
Does a lower RPN mean lower risk?
Not always. The product of three ordinal ratings hides differences between combinations. Review severity separately and use Action Priority if your customer requires AIAG and VDA 2019.
Can I change severity after an action?
Only if the design or process change alters the effect, for example by removing the hazard. Detection and prevention controls do not change severity.
Why does the chart fall in a straight line?
With severity and occurrence fixed, RPN rises linearly with detection. The slope equals severity times planned occurrence.
If your FMEA lives in spreadsheets, Netray can help link failure modes to ERP nonconformance and inspection data so ratings are based on real history.
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