FMEA RPN Calculator

The FMEA RPN Calculator scores a list of failure modes and ranks them. You enter one row per mode with its severity, occurrence and detection ratings on the usual 1 to 10 scales, and it computes each mode's risk priority number, sorts the list into priority bands against thresholds you set, and escalates any mode whose severity alone is high enough to demand attention regardless of its score.

It reports how many modes fall in each band, the highest and mean risk priority numbers, the largest severity-by-occurrence product, and how much of the total risk is concentrated in the top three modes.

Use it to triage an FMEA worksheet. This is the classic risk priority number method, which is deliberately not the Action Priority approach that the current AIAG-VDA handbook uses in its place.

Purpose and model boundary

This calculator ranks up to 15 entered failure modes with the traditional FMEA risk priority number (RPN), summarizes the distribution of risk, and applies user-authored high, medium, and severity-escalation thresholds. It is a prioritization aid. It does not perform an AIAG-VDA Action Priority lookup, prove that controls are effective, establish an acceptable residual risk, or certify an FMEA.

Inputs and units

Each used grid row contains an item label, a failure-mode label, and integer severity (S), occurrence (O), and detection (D) ratings from 1 through 10. A row is either complete or wholly blank: blank rows are unused capacity, while a partly filled row is rejected before calculation. Labels are descriptive; the arithmetic is driven by the three ratings. The high- and medium-priority thresholds are RPN values from 1 through 1000. The severity-escalation threshold is a rating from 1 through 10. The high RPN threshold must exceed the medium threshold.

Governing relationships

For each entered mode i, the workbook calculates

• RPN_i = S_i * O_i * D_i;
• Criticality_i = S_i * O_i;
• SeverityGate_i = 1 when S_i >= severity threshold, otherwise 0.

The priority band is evaluated in this order:

1. High when RPN_i >= high threshold or the severity gate is true;
2. Medium when it is not High and RPN_i >= medium threshold;
3. Low otherwise.

The summary uses MAX, SUM, and the arithmetic mean of positive RPN rows. Modes are ranked with Excel RANK. The reported top-three share is sum(RPN_i where rank_i <= 3) / total RPN; tied modes at the third rank are all included.

Calculation sequence

1. Read every row's three ratings and compute RPN, criticality, severity-gate flag, priority band, and rank.
2. Count positive-RPN rows and summarize maximum, mean, total, and counts by priority band.
3. Count modes escalated by severity whose RPN would otherwise remain below the high threshold.
4. Compute the maximum criticality and the ranked top-three share.
5. Send the per-mode RPN and criticality series to the comparison chart.

Outputs and interpretation

The highest and total RPN values show scale and aggregate exposure, while the mean gives context across the entered set. High/medium/low counts reflect the thresholds selected for this analysis, not universal boundaries. The severity-gate-only count identifies modes whose possible harm elevates them despite a lower product score. Criticality deliberately excludes detection; it emphasizes how severe and frequent a failure is before detection controls are considered.

Validation and status logic

The workbook evaluates status in this order:

The input rules additionally declare S, O, and D as integers bounded from 1 through 10, declare the RPN threshold bounds, and treat blanks in all five fields as forbidden once any field in that row is entered. Wholly blank rows remain legal spare capacity. Those input checks occur before the workbook status formula.

Assumptions and limitations

RPN multiplication gives equal mathematical weight to three ordinal ratings and can assign the same product to very different risk profiles. The custom severity gate mitigates one weakness but is not the licensed AIAG-VDA Action Priority method. Ratings depend on the team's definitions, evidence, and calibration; scores from different organizations are not automatically comparable. The top-three share includes all ties at rank three and can therefore cover more than three rows. Every scored row must carry both labels so the result remains identifiable and actionable.

Restrictions and non-computing states

The workbook accepts only the authored number of FMEA rows and the rating bounds it publishes. It does not compute the licensed AIAG-VDA Action Priority method. A partly filled row is rejected by the input rules; a wholly blank row is ignored. Missing or out-of-range severity, occurrence, or detection ratings that reach the workbook produce a non-computing state identified by the status message.

Errors and warnings

A rejected entry means a rating, limit, or grid entry did not meet the published input rules. A workbook NOT VALID result means the entered set or thresholds cannot be classified consistently. This workbook has no CHECK branch: a valid entered set returns OK, but that does not imply that the risk is acceptable. A connection or calculation-service failure is a service error rather than an FMEA finding.

The workbook derives its relations rather than reproducing any table, chart or figure from a specification, standard or agency publication. The risk priority number is a product of three ratings and the banding is a comparison against thresholds you set; no rating scale definitions are reproduced here.

• AIAG. New AIAG-VDA FMEA Handbook, which replaced risk priority number thresholds with Action Priority tables. https://blog.aiag.org/new-aiag-vda-fmea-handbook-and-trainings-available
• AIAG-VDA FMEA white paper, on the transition from RPN to Action Priority. https://www.aiag.org/docs/default-source/quality-/new_aiag_vda_fmea_-whitepaper.pdf?sfvrsn=6923e9d_4
• Wikipedia. Failure mode and effects analysis. https://en.wikipedia.org/wiki/Failure_mode_and_effects_analysis

The first two are cited to identify what this tool is not. If you are required to work to the AIAG-VDA handbook, its Action Priority tables are the method, and this calculator does not implement them.

Rating scale definitions (what a severity of 7 or an occurrence of 4 means for your product) come from your organisation's FMEA procedure. No trademark or organisation name appearing here implies endorsement by its owner.

Additional source notes migrated from Methodology

The workbook implements the traditional S * O * D RPN and S * O criticality relationships plus a custom user-set severity gate. It reproduces no proprietary FMEA table and makes no AIAG-VDA conformity claim; see the dedicated References section for licensing and non-endorsement details.