FMEA RPN Calculator
Calculate Risk Priority Number from Severity, Occurrence, and Detection ratings. Includes AIAG-VDA Action Priority classification.
Risk Ratings
Rating Reference
| Rating | Severity | Occurrence | Detection |
|---|---|---|---|
| 1 | No effect | Failure eliminated | Almost certain detection |
| 2-3 | Minor — slight inconvenience | Remote — rare failures | High — likely detected |
| 4-6 | Moderate — customer dissatisfied | Moderate — occasional | Moderate — may detect |
| 7-8 | High — significant impact | High — repeated failures | Low — unlikely detected |
| 9-10 | Very high — safety/regulatory | Very high — near certain | Very low — no detection |
What Is RPN (Risk Priority Number)?
Risk Priority Number is the core metric of Failure Mode and Effects Analysis (FMEA). It quantifies the risk of each potential failure mode by multiplying three factors: Severity (impact on the customer), Occurrence (how often the cause happens), and Detection (how well current controls catch it before it reaches the customer). RPN = S × O × D, producing a score from 1 to 1,000.
FMEA originated in the U.S. military (MIL-P-1629, 1949) and was adopted by the automotive industry through AIAG. Today it is required by IATF 16949, AS9100 (aerospace), and ISO 14971 (medical devices). RPN provides a repeatable, team-based method for prioritizing corrective actions on the failure modes that matter most.
RPN vs. Action Priority (AIAG-VDA)
Traditional RPN has a well-known weakness: it treats S, O, and D as interchangeable. A failure with S=10, O=1, D=1 (catastrophic but rare, easily detected) gets RPN=10 — the same as S=1, O=2, D=5 (trivial). The 2019 AIAG-VDA FMEA Handbook addressed this by introducing Action Priority (AP), a lookup-based classification that weighs Severity more heavily. Any failure with S ≥ 9 and O ≥ 4 is automatically High priority regardless of Detection. This calculator shows both RPN and AP so you can compare the traditional and modern approaches.
How to Reduce a High RPN
Severity is usually fixed by the product design, so focus on the two factors you can control:
- Reduce Occurrence — eliminate the root cause with design changes, poka-yoke (mistake-proofing), or process parameter optimization. Use Pareto analysis to identify which causes drive the most failures.
- Reduce Detection — improve your ability to catch failures before they reach the customer. Add in-process SPC, automated inspection, or 100% functional testing. A control chart can detect process shifts before they produce defects.
- Track before and after — re-score each failure mode after implementing actions. The RPN delta demonstrates improvement to auditors and management.
FMEA in Practice
Effective FMEA is a living document, not a one-time exercise. Update it when designs change, new failure modes are discovered, or corrective actions are implemented. For persistent FMEA tracking with Bayesian evidence linking, automatic RPN recalculation, and PDF export, use the full FMEA tool in Svend.
- Automotive (IATF 16949) — Design FMEA (DFMEA) and Process FMEA (PFMEA) required for PPAP submission
- Aerospace (AS9100) — FMEA required for critical and safety characteristics
- Medical devices (ISO 14971) — Risk analysis using FMEA methodology for hazard identification
- General manufacturing — FMEA drives preventive action and continuous improvement per ISO 9001 clause 6.1
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