When Automotive FMEAs consider criticality, values of 1 to 10 are assigned to severity, detection and occurrence, with 10 being the most severe, the least detected or the most frequently occurring item. A criticality value known as a Risk Priority Number (RPN) is then calculated for each failure mode by taking the product of these three values:

RPN = Severity X Detection X Occurrence

When standard rating scales are used, RPNs have values between 1 and 1000. Higher RPNs indicate more critical failure modes. Therefore, RPNs should be sorted from highest to lowest values so that immediate attention can be given to those failure modes with the highest RPNs values. The RPN results can then be used for analysis.

When detection values are high, RPNs may be high for failure modes that are less than critical in respect to quality, reliability and safety.