Risk Matrix and RPN Calculator: Formula, Example & Instant Result
A risk matrix ranks a failure mode by how serious its effect is (severity) and how often it happens (occurrence). The risk priority number (RPN) also multiplies in how well your controls detect it. Both are ranking aids that help you decide what to work on first — not proofs that a risk is acceptable.
↳ Values are pre-filled with an example — replace them with your own data.
Your data
Severity
4 = function lost or safety-related function degraded
Occurrence
3 = occasional
Detection
2 = high chance of detection
Bands are this tool's default convention — organizations should set their own thresholds.
Result
S×O scoreHigh12
How serious and how frequent — the risk before your controls.
RPNMedium24
Ranking aid that also counts how well your controls detect it.
Detection is masking a serious risk: the RPN band is lower than the S×O band. RPN is a ranking aid, never a permission slip.
Recommended action
Act now: contain if needed, then reduce occurrence (error-proofing, process change) before relying on detection.
RPN on the 1–125 scale
4 × 3 × 2 = 24 / 125
Detection 2 puts the RPN in the Medium band.
5×5 risk matrix with the selected cell at severity 4, occurrence 3 (S×O 12); RPN 24 out of 125 shown on the bar.
A wrong torque on a brake-line fitting is rated in a process risk review. How urgent is it?
Data
• Severity S = 4 (safety-related function degraded)
• Occurrence O = 3 (occasional)
• Detection D = 2 (100 % torque check with a monitored tool)
Step by step
1S×O = 4 × 3 = 12 → high
2RPN = 4 × 3 × 2 = 24 → medium
3The RPN band is lower than the S×O band: detection is masking the risk
What it means
By RPN alone this looks like a medium risk, but S×O says high: the failure is serious and happens occasionally, and only a good check keeps it from the customer. RPN is a ranking aid, never a permission slip. Act on the high S×O: reduce occurrence first (error-proof the tightening), keep the check, and review the rating after the change.
Tips & common mistakes
▲Rate severity on the effect for the end user, not on how hard it is to fix.
▲Agree the scale definitions in writing before the session so ratings are comparable.
▲Rate occurrence from data (complaints, scrap, field returns) whenever you have it.
▲Detection is the ability of your current controls to catch the failure before it leaves — not luck in final testing.
▲AI assistants often rank purely by RPN; check the S×O score and the masking warning here before deciding.
AI prompt for this calculation
Paste it into your AI assistant to be walked through the calculation with your own data.
Act as a risk management facilitator and help me rate and prioritize a failure mode.
Use exactly these formulas:
S×O score = severity × occurrence (1–25)
RPN = severity × occurrence × detection (1–125), all on 1–5 scales
Default bands: S×O 1–4 low, 5–9 medium, 10–16 high, 17–25 critical; RPN 1–23 low, 24–59 medium, 60–99 high, 100–125 very high (tell me these are only a default convention).
Rules:
1. Restate my ratings and the reason for each before calculating.
2. If any rating or its justification is missing or unclear, ask me — never assume.
3. If the RPN band is lower than the S×O band, warn me that detection is masking a serious risk.
4. Recommend actions by band: for critical or high, containment and occurrence reduction first.
5. Never treat a low RPN as permission to skip action on a high-severity failure.
My failure mode:
Description =
Severity (1–5) and why =
Occurrence (1–5) and why =
Detection (1–5) and why =
The buttons copy the prompt first, then open the assistant in a new tab.
Add this calculator to your site
Copy the code below into your page. The calculator stays free; keep the attribution link with it.
<iframe src="https://www.qualityforeveryone.com/embed/calculators/en/risk-matrix-rpn-calculator" title="Risk Matrix / RPN — Quality for Everyone" width="100%" height="1100" style="border:0;max-width:100%" loading="lazy"></iframe>
<p><a href="https://www.qualityforeveryone.com/en/lab/calculators/risk-matrix-rpn-calculator">Risk Matrix / RPN calculator by Quality for Everyone</a></p>
Next step · DOCAMIN
Open a risk register entry and route this into your FMEA document in DOCAMIN.
Because very different risks can share a number. Severity 5, occurrence 5, detection 1 gives RPN 25 — the same band as a trivial nuisance — although the failure is catastrophic and frequent and only a perfect check stops it. Always look at severity and S×O before the RPN.
Should I decide by S×O or by RPN?
+
Use S×O to decide whether the risk itself is tolerable and how urgently the design or process must change. Use RPN to rank actions among risks with similar S×O. A common rule is: any high severity gets action regardless of RPN.
1–5 or 1–10 scales — which is better?
+
Both are widely used. Ten-point scales give finer steps but invite false precision and long debates; five-point scales are faster and more consistent between teams. Whatever you choose, define every value in words and do not mix scales in one register. This tool uses 1–5.
What does detection actually cover?
+
The ability of the controls you already have — inspections, tests, error-proofing, monitoring — to catch the cause or the failure before it reaches the customer. It does not cover hoping a final test happens to notice. Better detection lowers the RPN but not the risk itself.
Last tested: October 2026 · Tested with: automated math tests (3+ cases) · Reviewed by: Quality for Everyone editorial team
