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.

Inputs

Severity of the effect

Likelihood of the cause occurring

Ability of the current control to detect the cause

Your action threshold for RPNpoints

Failure has safety or regulatory consequences

Risk Priority Number

240of 1000

Criticality (S × O)

40of 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

Values used
Severity of the effect = 8 — Very high, system inoperable; Likelihood of the cause occurring = 5 — Occasional; Ability of the current control to detect the cause = 6 — Low; Your action threshold for RPN = 100 points; Failure has safety or regulatory consequences = No
Risk Priority Number
RPN = severity × occurrence × detection, each rated 1–10, giving a range of 1 to 1000; criticality = severity × occurrence.
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.
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

How it works

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

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.

You might also need

Risk Heatmap Calculator Control Effectiveness Calculator Residual Risk Calculator