Calculate Risk Priority Numbers (RPN) for Failure Mode and Effects Analysis. Prioritize failure modes by severity, occurrence, and detection ratings.
Failure Mode and Effects Analysis (FMEA) is a systematic method for evaluating potential failures in a product or process. Each failure mode is assessed on three dimensions: Severity (S) — how serious is the effect; Occurrence (O) — how likely is the failure to happen; and Detection (D) — how likely is it that the failure will be detected before reaching the customer.
The Risk Priority Number (RPN) is the product of these three ratings (each on a 1–10 scale), yielding a value from 1 to 1,000. Higher RPNs indicate higher risk and higher priority for corrective action. While RPN is not a perfect risk measure (it has known limitations), it remains the most widely used prioritization tool in FMEA.
This calculator computes the RPN and provides guidance on the risk level, helping FMEA teams prioritize which failure modes to address first.
By calculating this metric accurately, production managers gain actionable insights that drive continuous improvement efforts and strengthen overall operational performance across the shop floor.
RPN provides a single numeric priority for each failure mode, enabling FMEA teams to rank risks objectively and focus corrective actions on the highest-priority items. Data-driven tracking enables proactive decision-making rather than reactive problem-solving, ultimately saving time, materials, and labor costs in production operations. This quantitative approach replaces subjective estimates with hard data, enabling confident planning decisions and more effective resource allocation across production operations.
RPN = Severity (S) × Occurrence (O) × Detection (D) Each rating: 1 to 10 RPN range: 1 to 1,000 Risk levels: • RPN ≥ 200 — High risk (action required) • RPN 100–199 — Medium risk (action recommended) • RPN < 100 — Low risk (monitor)
Result: RPN = 192
S = 8 (significant impact), O = 4 (occasional occurrence), D = 6 (moderate detection). RPN = 8 × 4 × 6 = 192. This is a medium-high risk that should be addressed with corrective action.
FMEA should begin early in the design phase and continue through process development, production launch, and ongoing production. Early identification of failure modes enables design changes that are far cheaper than manufacturing corrections.
The AIAG-VDA FMEA handbook introduced Action Priority (AP) as an alternative to RPN. AP uses a three-level rating (High/Medium/Low) determined by a lookup table considering S, O, and D together, addressing RPN's mathematical limitations.
For each high-priority failure mode, define: recommended action, responsibility, target date, action taken, and revised S/O/D ratings. Track action completion and verify that the revised RPN or AP is acceptable.
There is no universal threshold. Many organizations use 100 or 200 as a trigger. However, AIAG recommends focusing on the highest RPNs relative to the full list rather than a fixed cutoff. Always prioritize high Severity items.
RPN treats S, O, and D as equally important, which is debatable — S=10 O=1 D=1 (RPN=10) may be more critical than S=2 O=5 D=5 (RPN=50). RPN also has non-linear gaps in achievable values (e.g., no RPN=39 is possible).
Design FMEA (DFMEA) analyzes potential design failures and their effects. Process FMEA (PFMEA) analyzes potential manufacturing process failures. Both use the same S×O×D methodology but focus on different failure sources.
Detection rates the likelihood that current controls will detect the failure before it reaches the customer. D=1 means detection is virtually certain (e.g., automated 100% testing). D=10 means no detection mechanism exists.
The AIAG-VDA FMEA handbook (2019) replaces RPN with Action Priority (AP) — High, Medium, or Low — based on a lookup table that better handles the non-linearity issue. The S, O, D ratings are still used.
FMEA is a living document. Update it when: the design or process changes, new failure modes are discovered, corrective actions are implemented, or customer complaints reveal new risks. Review at least annually.