What RPN value requires action?

No threshold is universal, and AIAG explicitly discourages threshold-only decision making. Common practice is to act on every severity 9–10 mode regardless of RPN, then work down the ranked list until risk is tolerable.

What replaced RPN in AIAG-VDA?

The 2019 AIAG-VDA handbook introduced Action Priority (AP), which maps S, O and D combinations to High, Medium or Low priority via a lookup table rather than a product. It avoids the false precision of multiplying ordinal scales. Many organisations still report both.

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FMEA RPN Calculator

The Risk Priority Number ranks failure modes so a team can decide what to work on first. It is the product of three 1–10 ratings: how bad the failure is, how often the cause occurs, and how likely current controls are to catch it before the customer does.

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Formula

Risk Priority NumberRPN = S × O × D

Each rating runs 1–10, so RPN ranges from 1 to 1000.

CriticalityCriticality = S × O

Ignores detection — useful when you want design risk rather than control-plan risk.

Rating scales

Severity (S)	Consequence of the failure effect. 10 = hazardous without warning or regulatory non-compliance; 1 = no discernible effect.
Occurrence (O)	Likelihood the cause happens. 10 = failure is almost inevitable; 1 = failure eliminated by preventive control.
Detection (D)	Likelihood current controls detect the cause or mode before release. 10 = no control or control will not detect; 1 = control detects with near certainty.

Worked example

A gearbox oil seal leaks. The team rates severity 8 (loss of primary function, machine stops), occurrence 4 (seal failures seen occasionally in similar units), detection 6 (leak only found on walkdown, not by instrumentation).

RPN = 8 × 4 × 6 = 192
Criticality = S × O = 8 × 4 = 32
Adding a level switch improves detection from 6 to 2.
Revised RPN = 8 × 4 × 2 = 64

A single detection control cuts the RPN by two thirds without touching the design. Note severity stayed at 8 — severity only changes if the design or the effect changes, never through better detection.

Run this with your own numbers

Common mistakes

Using a single RPN threshold (typically 100) as the sole trigger for action. A severity-10 mode with RPN 80 is more dangerous than a severity-3 mode with RPN 200.
Reducing severity because a control was added. Detection controls change D, never S.
Treating RPN as a measurable quantity. The ratings are ordinal, so the product is a ranking aid, not a risk figure you can average or trend.
Rating occurrence from opinion when field or warranty data exists.

Frequently asked questions

What RPN value requires action?: No threshold is universal, and AIAG explicitly discourages threshold-only decision making. Common practice is to act on every severity 9–10 mode regardless of RPN, then work down the ranked list until risk is tolerable.
What replaced RPN in AIAG-VDA?: The 2019 AIAG-VDA handbook introduced Action Priority (AP), which maps S, O and D combinations to High, Medium or Low priority via a lookup table rather than a product. It avoids the false precision of multiplying ordinal scales. Many organisations still report both.

About Reliability Pro

FMEA RPN is part of a suite of 126 reliability, maintenance and quality engineering tools covering life data analysis, accelerated testing, system reliability, FMEA and root cause, SPC, and design for reliability. It runs in the browser and as native iOS and Android apps, so the same calculation is available at a desk or in front of the asset.

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