Risk Priority Number (FMEA) Calculator
Calculate the FMEA Risk Priority Number (RPN) by multiplying your Severity, Occurrence and Detection ratings, and see the indicative priority band. A quick way to rank failure modes during a Failure Mode and Effects Analysis so the team can focus corrective action where it matters most.
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Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Rate Severity (S) 1–10 — how serious the effect of the failure is (10 = catastrophic / safety hazard).
- Rate Occurrence (O) 1–10 — how likely the cause is to happen, and Detection (D) 1–10 — how likely your current controls are to MISS it (10 = almost never caught).
- Read the RPN (S × O × D, 1–1000) and the indicative band, then compare against your own FMEA thresholds.
How it works
The Risk Priority Number is simply RPN = Severity × Occurrence × Detection. Because each factor runs 1–10, the RPN ranges from 1 (a trivial, obvious, near-impossible failure) to 1000 (severe, frequent and undetectable). Higher is worse. The bands shown (RPN ≥ 200 High, 100–199 Medium, below 100 Low) are only a starting point — real FMEA procedures set their own thresholds and often act on high Severity alone.
Worked example
Worked example. A pump seal failure is rated Severity 8 (major leak), Occurrence 5 and Detection 6 (hard to catch before it leaks). RPN = 8 × 5 × 6 = 240, which falls in the indicative High band, flagging it for priority corrective action. Improving detection to a rating of 2 would drop the RPN to 80.
Common mistakes
- Reading the Detection scale backwards — a HIGH detection rating (10) means the problem is almost never caught, which INCREASES the RPN. Good controls score low.
- Treating equal RPNs as equal risk. 2 × 2 × 10 and 10 × 2 × 2 both give 40, but a Severity-10 failure is far more serious — always review the individual ratings.
- Chasing RPN alone and ignoring high Severity. A safety-critical failure (Severity 9–10) usually warrants action even if its RPN is modest.
Frequently asked questions
What is a 'good' or 'safe' RPN threshold?
There is no universal figure. The ≥ 200 / 100–199 / < 100 bands here are indicative only. Your FMEA procedure should define the thresholds and, importantly, mandate action on any high-Severity item regardless of its RPN.
Does this replace a formal FMEA or risk assessment?
No. It only does the arithmetic. A valid FMEA needs a competent multi-disciplinary team, agreed rating scales, and documentation to the applicable standard (for example IEC 60812) — this tool does not replace that or your regulator's requirements.
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