FMEA Risk Priority Number Calculator

Content

Screen and rank failure modes with classic Severity × Occurrence × Detection risk priority numbers, before and after planned controls.

Engineering screening tool—verify inputs and results independently. Use at your own risk.

Failure-mode ratings

How to use

  1. Name one failure mode and optionally record its effect, cause, action, and owner.
  2. Rate Severity, Occurrence, and Detection with one documented organizational 1–10 scale. Detection 10 means least detectable.
  3. Enter expected post-action ratings. Do not reduce severity unless the action truly reduces the consequence.
  4. Keep or edit the local Low/High thresholds. These bands are configurable screening aids, not AIAG/VDA Action Priority.
  5. Select Calculate and add to update the canonical result and append the row to the ranked register.
  6. Interpret high severity independently of RPN; equal RPN values can represent very different risk profiles.
  7. Use Export CSV after adding rows, or Reset to clear the register and restore the example.
  8. Do not use this model as a substitute for a controlled FMEA process, standard-specific Action Priority tables, quantitative reliability analysis, or safety/risk acceptance.

Equations used

For integer ratings S, O, D ∈ {1,…,10}, the initial risk priority number is RPN = S × O × D. Revised ratings give RPN₂ = S₂ × O₂ × D₂. The absolute change is ΔRPN = RPN − RPN₂, and relative reduction is 100 ΔRPN / RPN percent. Rows are sorted by descending initial RPN; ties share competition rank. Local bands are Low when RPN ≤ L, Medium when L < RPN < H, and High when RPN ≥ H.

Worked example

  1. Gear micropitting is rated S=9, O=6, D=7.
  2. The initial result is 9 × 6 × 7 = 378, High with the example local thresholds.
  3. After filtration and lubricant controls, S₂=9, O₂=3, D₂=3 gives 81.
  4. The reduction is 297 or 78.6%. Severity remains 9, so the team must still manage the consequence explicitly despite the lower RPN.

Theory and method

FMEA is a structured team method for identifying failure modes, consequences, causes, and controls. Classic RPN multiplies three ordinal ratings, producing an integer from 1 to 1000. Because multiplication is not a calibrated probability or loss model, the number is best used to organize review within one consistently rated FMEA—not to compare unrelated organizations, rating tables, or products. The configurable bands on this page are deliberately labeled local; official AIAG/VDA Action Priority uses a separate standard-specific decision table and is not reproduced here.

Bruker

Assumptions and limits: use one controlled rating scale; preserve severe consequences in decision-making; reassess ratings with evidence; and review common-cause, safety, regulatory, environmental, and uncertainty effects outside this arithmetic. The calculator does not estimate failure probability, financial consequence, residual risk acceptance, or confidence.

References: IEC 60812:2018, Failure modes and effects analysis (FMEA and FMECA); SAE J1739, Potential Failure Mode and Effects Analysis; and the ReliabilityCalc FMEA page for independent formula-background comparison. For detailed contact, lubrication, or wear mechanisms identified by the FMEA, refine the engineering model in TriboSolver.