Hazard Risk Priority Number (RPN) Calculator
Calculate the Hazard Risk Priority Number (RPN) used in Failure Mode and Effects Analysis (FMEA) and hazard risk assessments. RPN helps prioritize risks by combining Severity, Probability of Occurrence, and Detectability scores.
1 = No effect | 10 = Catastrophic
1 = Extremely unlikely | 10 = Almost certain
1 = Almost certain to detect | 10 = Undetectable
Formula
RPN = S × P × D
- S (Severity): Rates the seriousness of the hazard's effect on a scale of 1–10.
- P (Probability of Occurrence): Rates the likelihood that the hazard will occur on a scale of 1–10.
- D (Detectability): Rates how difficult it is to detect the hazard before harm occurs on a scale of 1–10 (10 = hardest to detect).
- RPN range: 1 (minimum risk) to 1,000 (maximum risk).
Risk Thresholds (common industry guidance):
- RPN ≥ 200 → Critical Risk — Immediate action required
- RPN 125–199 → High Risk — Priority corrective action
- RPN 50–124 → Moderate Risk — Action plan recommended
- RPN 10–49 → Low Risk — Monitor and review
- RPN 1–9 → Negligible Risk — Acceptable, document only
Assumptions & References
- All three inputs (S, P, D) must be integer values between 1 and 10 inclusive, consistent with standard FMEA rating scales.
- The RPN method is defined in IEC 60812:2018 (Failure modes and effects analysis) and widely used in ISO 14971 (medical devices), AIAG FMEA standards (automotive), and MIL-STD-882 (system safety).
- Detectability is scored inversely: a score of 1 means the hazard is almost certain to be detected; 10 means it is virtually undetectable.
- RPN thresholds used here are based on common industry practice and may vary by organization, sector, or regulatory framework. Always consult your organization's risk acceptance criteria.
- RPN alone does not capture all risk dimensions. High-severity items with low RPN may still require mitigation. Use RPN alongside qualitative risk matrices for comprehensive assessment.
- Reference: AIAG & VDA FMEA Handbook (2019); IEC 60812:2018; ISO 14971:2019.