FMEA Scoring: which formula represents the Risk Priority Number (RPN)?

• A. Severity + Probability + Detection
• B. Severity x Probability + Detection
• C. Severity x Probability x Detection
• D. Severity x Detection x Occurrence

Answer: (C)

RPN is meant to capture how bad a potential failure could be, how likely it is to occur, and how likely current controls are to detect it before it reaches the patient. Because risk compounds across these three dimensions, they are multiplied to form the Risk Priority Number. In practice, Severity × Occurrence × Detection is the standard formula. Probability is another term for Occurrence, so Severity × Probability × Detection corresponds to the same RPN. The idea is not simply to add the factors or to exclude one dimension; multiplying all three ensures a high RPN only when all aspects are high, and it ranks issues by overall risk. For example, if severity is 8, occurrence 5, and detection 3, the RPN is 8 × 5 × 3 = 120.