Risk Priority Number Calculator

Compute an FMEA risk priority number from severity, occurrence and detection on the 1–10 scales, with criticality and an action priority.

About Risk Priority Number Calculator

The detection scale is inverted — 1 means you will certainly catch it, 10 means you have no chance — so a high RPN can come from a genuinely dangerous failure or merely from a blind spot in monitoring. Criticality is reported alongside because it drops detection entirely, which stops a team from adding an inspection step to make a dangerous failure mode look acceptable. RPN is the standard way to rank failure modes in an FMEA and it works well as a queue, but it is an ordinal product, not a measurement, so a 200 is not twice as bad as a 100. Use it to order the work, then argue about the top of the list.

Formulas

Risk Priority Number

RPN = severity × occurrence × detection, each rated 1–10, giving a range of 1 to 1000; criticality = severity × occurrence.

severity: How bad the effect is, 1–10
occurrence: How often the cause happens, 1–10
detection: How poorly the current control detects it — 10 means no detection at all

Action priority

Action priority follows the AIAG-VDA style logic: high severity with any real occurrence, or a large RPN, demands action regardless of the arithmetic.

criticality: Severity × occurrence, which ignores detection and so cannot be gamed by adding inspection
S ≥ 9: Hazardous effects are actioned on severity alone

Worked example

With the default values below, Risk Priority Number Calculator returns Risk Priority Number of 240. Change any input above and every figure here is recalculated in your browser.

Inputs used

Severity of the effectone of 1 — No discernible effect, 2 — Very minor, 3 — Minor, 4 — Very low, 5 — Low, noticeable degradation, 6 — Moderate, partial loss of function, 7 — High, loss of primary function, 8 — Very high, system inoperable, 9 — Hazardous with warning, 10 — Hazardous without warning: 8 — Very high, system inoperable
Likelihood of the cause occurringone of 1 — Practically impossible, 2 — Remote, 3 — Very slight, 4 — Slight, 5 — Occasional, 6 — Moderate, 7 — Frequent, 8 — High, 9 — Very high, 10 — Almost certain: 5 — Occasional
Ability of the current control to detect the causeone of 1 — Detection almost certain, 2 — Very high, 3 — High, 4 — Moderately high, 5 — Moderate, 6 — Low, 7 — Very low, 8 — Remote, 9 — Very remote, 10 — No detection capability: 6 — Low
Your action threshold for RPNaccepts 1–1,000 points: 100 points
Failure has safety or regulatory consequences: No

Results

Risk Priority Number: 240 of 1000
Criticality (S × O): 40 of 100
Share of the Maximum RPN: 24.0%
Action Priority: High — action required, and a decision not to act must be justified in writing
Threshold Verdict: Above your threshold of 100 — raise a corrective action with an owner and a date
Where to Act: Severity — the only real fix is design change, because severity is a property of the effect and cannot be inspected away
Safety and Regulatory Note: No safety or regulatory flag, so RPN ranking alone is a reasonable basis for prioritisation

Step by step

1Values used
2Risk Priority Number
3Action priority
4Risk Priority Number= 240 of 1000
5Criticality (S × O)= 40 of 100
6Share of the Maximum RPN= 24.0
7Action Priority= High — action required, and a decision not to act must be justified in writing
8Threshold Verdict= Above your threshold of 100 — raise a corrective action with an owner and a date
9Where to Act= Severity — the only real fix is design change, because severity is a property of the effect and cannot be inspected away

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Risk Priority Number calculated?

RPN = severity × occurrence × detection, each rated 1–10, giving a range of 1 to 1000; criticality = severity × occurrence. The detection scale is inverted — 1 means you will certainly catch it, 10 means you have no chance — so a high RPN can come from a genuinely dangerous failure or merely from a blind spot in monitoring. Criticality is reported alongside because it drops detection entirely, which stops a team from adding an inspection step to make a dangerous failure mode look acceptable.

Why does Risk Priority Number matter?

RPN is the standard way to rank failure modes in an FMEA and it works well as a queue, but it is an ordinal product, not a measurement, so a 200 is not twice as bad as a 100. Use it to order the work, then argue about the top of the list.

What values do I need to enter?

This calculator takes 5 inputs: Severity of the effect, Likelihood of the cause occurring, Ability of the current control to detect the cause, Your action threshold for RPN, Failure has safety or regulatory consequences. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.

Is RPN a reliable way to rank risks?

It ranks reasonably and measures badly. The scales are ordinal, so multiplying them produces gaps and duplicates — 120 can be reached six different ways with very different meanings. That is why the newer AIAG-VDA method replaced RPN thresholds with an action priority table, and why criticality and severity are shown here alongside the number.

Why does severity alone sometimes force action?

Because you cannot inspect your way out of a hazardous failure. If the effect is severity 9 or 10, the acceptable responses are design change or elimination of the cause; improving detection only means you find out sooner that someone was hurt.