RPN stands for Risk Priority Number, which is a numerical assessment of the risk priority level of a failure mode or failure cause in an FMEA analysis. It is a score that reflects the severity, occurrence, and detection of each failure mode. The RPN is calculated by multiplying the Severity (S), Occurrence (O), and Detection (D) ratings for a particular failure mode, RPN = S x O x D. The RPN is used to prioritize which risks to accept and which to address. However, using only the RPN to determine the failure mode that requires corrective action can cause severe quality problems in an organization. Therefore, companies that wish to avoid the limitations of the RPN should evaluate risk with a combination of other indexes, such as the Critical Number (CN) or Severity-Occurrence-Detection (SOD) .