Risk Priority Number (RPN)

The Risk Priority Number is a quantitative scoring system used in FMEA that multiplies three independently assessed factors — Severity (S), Occurrence (O), and Detection (D) — each rated 1-10, to produce a composite risk score ranging from 1 to 1000. S=10 means catastrophic failure; O=10 means failure is almost certain; D=10 means the failure is virtually undetectable before reaching the end user. The RPN directs attention and resources to failure modes that combine seriousness, likelihood, AND difficulty of detection. A frequent but easily caught defect (S=5, O=8, D=2, RPN=80) is less urgent than an infrequent but undetectable critical failure (S=9, O=3, D=9, RPN=243). Practitioners use RPN not as an absolute measure but as a relative ranking tool: which failure modes need attention first? After implementing corrective actions, the team re-scores to verify that the RPN has decreased.

When to use it

When prioritizing among multiple risks that differ in severity, probability, and detectability; when allocating limited risk-mitigation resources; when evaluating whether corrective actions actually reduced risk; or when you need a structured framework for cross-functional risk discussion.

How it can help

RPN's three-factor scoring is applicable wherever you need to prioritize among multiple risks. Most people intuitively prioritize by severity alone ('fix the worst thing first') or probability alone ('fix the most likely thing first'). Adding detection — 'how likely are we to catch this before it causes harm?' — transforms risk prioritization. A moderate-severity, moderate-probability risk that is essentially invisible to your monitoring systems may be far more dangerous than a severe, frequent risk that your quality systems reliably catch. The model teaches that investment in detection capability is itself a form of risk reduction, independent of reducing probability or mitigating severity.