Calculation reviewed: 4 October 2026 · Engineering Desk Tools
How to use the FMEA risk priority number calculator
Multiply severity, occurrence and detection ratings to get a risk priority number for a failure mode. Start with measurements or documented values for the equipment and reporting period you actually want to assess. The calculator does not fill in a typical installation for you. Its blank fields help keep a demonstration value from being mistaken for your own operating data.
Choose the required options, enter the values in the labelled units and select Calculate. If a field is rejected, check its range and unit before changing it. The result is accompanied by the equation and assumptions so you can decide whether it answers your engineering question.
Inputs and measurement basis
- Severity rating (1 to 10). How serious the effect of the failure is. 10 is the most severe, such as a safety effect. Allowed range: 1 to 10.
- Occurrence rating (1 to 10). How likely the cause is to occur. 10 means very frequent. Allowed range: 1 to 10.
- Detection rating (1 to 10, 10 = hard to detect). How unlikely the current controls are to detect the failure in time. 10 means almost undetectable. Allowed range: 1 to 10.
Record the measurement source and operating condition. Retain unrounded values for verification.
Method and interpretation
Failure mode and effects analysis ranks failure modes by multiplying three ratings: how severe the effect is, how often the cause occurs, and how hard the failure is to detect before it causes harm. Higher numbers mean higher priority. The ranking is only as good as the rating scales and the knowledge of the team that sets them.
RPN = Severity × Occurrence × Detection. The maximum is 10 × 10 × 10 = 1000.
Rate each factor with your own agreed scale, and use the same scale for every failure mode in the study. A high detection number means the failure is hard to detect. RPN has known limits: different combinations can give the same number, and a severe failure with a low RPN can be ignored. Review any failure with severity 9 or 10 regardless of the RPN. There is no universal action threshold; the team sets it. Many organizations now use action priority tables instead of a single RPN.
Worked example
This example does not populate the form. Enter your own installation data.
Calculated result: 160 RPN. Compare with your team action threshold and rank the failure modes. Re-rate after the corrective action is complete.
Check the arithmetic independently using the displayed equation. Retain intermediate precision and compare the final value with your equipment documentation.
Quick-reference table
These are illustrative values, not certified ratings or manufacturer data. Use the form for your own conditions.
Common mistakes
Using different scales for different failure modes; treating the RPN as a measurement rather than a ranking aid; ignoring a high-severity failure because the RPN is low; setting an action threshold without team agreement; forgetting to re-rate after the action. Before relying on the output, check the decimal format, unit scale and source of each value. Recheck unusual results against the formula.
Frequently asked questions
Are the example values used automatically?
No. Inputs remain blank when the tool opens or when you clear them. The worked example and table are reading material below the calculator. Enter the actual values you want to check each time, and label saved reports so their context is not lost.
What does the result mean?
The result ranks this failure mode against others scored on the same scales. A higher number means a higher priority, but always review severity 9 or 10 items regardless of the score.
Can I use a zero or a negative value?
The allowed range follows the meaning of each input. A divisor needs a positive value; other fields may allow zero. Check the form labels and error message rather than forcing an invalid value. A rejected input must be corrected before a result can be shown.
Is this a final design or equipment approval?
No. Rate each factor with your own agreed scale, and use the same scale for every failure mode in the study. A high detection number means the failure is hard to detect. RPN has known limits: different combinations can give the same number, and a severe failure with a low RPN can be ignored. Review any failure with severity 9 or 10 regardless of the RPN. There is no universal action threshold; the team sets it. Many organizations now use action priority tables instead of a single RPN. Use the calculation as support for a checked decision, and review equipment documentation and applicable requirements before changing an installation or operating setting.
How can I save or share a calculation?
Calculate first, then use Copy result or Print report. Some maintenance tools also provide a CSV summary. Reports contain your own entered data, so review them before sharing. You can share the public page URL without including plant records or confidential measurements.
How do I report an unexpected result?
Use the Contact page and include the tool URL, input values, units, expected output and the reference you used. Explain the measurement basis. Exclude confidential information.
Related tools and records
Use related calculations with consistent units, periods and equipment scope.
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