Compute an FMEA risk priority number from severity, occurrence and detection on the 1–10 scales, with criticality and an action priority.
The detection scale is inverted — 1 means you will certainly catch it, 10 means you have no chance — so a high RPN can come from a genuinely dangerous failure or merely from a blind spot in monitoring. Criticality is reported alongside because it drops detection entirely, which stops a team from adding an inspection step to make a dangerous failure mode look acceptable. RPN is the standard way to rank failure modes in an FMEA and it works well as a queue, but it is an ordinal product, not a measurement, so a 200 is not twice as bad as a 100. Use it to order the work, then argue about the top of the list.
Risk Priority Number
RPN = severity × occurrence × detection, each rated 1–10, giving a range of 1 to 1000; criticality = severity × occurrence.
Action priority
Action priority follows the AIAG-VDA style logic: high severity with any real occurrence, or a large RPN, demands action regardless of the arithmetic.
RPN = severity × occurrence × detection, each rated 1–10, giving a range of 1 to 1000; criticality = severity × occurrence. The detection scale is inverted — 1 means you will certainly catch it, 10 means you have no chance — so a high RPN can come from a genuinely dangerous failure or merely from a blind spot in monitoring. Criticality is reported alongside because it drops detection entirely, which stops a team from adding an inspection step to make a dangerous failure mode look acceptable.
RPN is the standard way to rank failure modes in an FMEA and it works well as a queue, but it is an ordinal product, not a measurement, so a 200 is not twice as bad as a 100. Use it to order the work, then argue about the top of the list.
This calculator takes 5 inputs: Severity of the effect, Likelihood of the cause occurring, Ability of the current control to detect the cause, Your action threshold for RPN, Failure has safety or regulatory consequences. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
It ranks reasonably and measures badly. The scales are ordinal, so multiplying them produces gaps and duplicates — 120 can be reached six different ways with very different meanings. That is why the newer AIAG-VDA method replaced RPN thresholds with an action priority table, and why criticality and severity are shown here alongside the number.
Because you cannot inspect your way out of a hazardous failure. If the effect is severity 9 or 10, the acceptable responses are design change or elimination of the cause; improving detection only means you find out sooner that someone was hurt.