Some risks are loud. Others sit quietly in a machine or a process until the day they fail. FMEA is a method that helps you find those failures before they cause harm, and the RPN is the number that tells you which ones to deal with first.
Enter your three scores below, and the calculator will give you the risk priority number straight away.
What is RPN?
RPN stands for Risk Priority Number. It is used in FMEA, which means Failure Mode and Effects Analysis. In FMEA, you list the ways something can fail, then score each one on three things. The result is a single number that lets you rank the failures from the most urgent to the least.
It is used in manufacturing, maintenance, quality control and safety work. If you want to know which of ten possible failures to fix first, this is a quick way to decide.
The RPN formula
RPN = Severity x Occurrence x Detection
Each factor is scored from 1 to 10, so the lowest RPN is 1 and the highest is 1,000.
What the three scores mean
- Severity (S): how bad the result is if the failure happens. A score of 1 means almost no effect. A score of 10 means a death or a very serious harm.
- Occurrence (O): how often the failure is likely to happen. A score of 1 means very unlikely. A score of 10 means it happens all the time.
- Detection (D): how likely you are to spot the problem before it does harm. This one works the opposite way. A score of 1 means you will almost always catch it. A score of 10 means you will almost certainly miss it.
The detection scale confuses many beginners. A high detection score is bad news, because it means the failure hides well.
Worked example
A factory has a conveyor with a safety guard. The team asks what happens if the guard sensor fails.
- Severity is 9, because a worker could be seriously hurt.
- Occurrence is 4, because the sensor has failed a few times in the past.
- Detection is 6, because the failure is only found in a monthly check.
RPN = 9 x 4 x 6 = 216
The team decides to add a daily check and a warning light that comes on when the sensor fails. Occurrence drops to 2 and detection drops to 3. Severity stays at 9, because the harm would be the same if the failure did happen.
New RPN = 9 x 2 x 3 = 54
The RPN fell from 216 to 54. That is a drop of 75 percent, and it is a number you can show in a report.
How to read your RPN
There is no single number that is right for every company. Many teams set a limit, such as 100 or 125, and act on anything above it. Others simply sort the list and fix the highest numbers first. Pick a method, write it down and use it every time.
As a rough guide, you can think of it this way:
- Under 100: low priority, review during normal checks
- 100 to 200: medium priority, plan an action
- Over 200: high priority, act soon
Whatever limit you pick, always look at severity on its own as well. A failure with a severity of 9 or 10 needs action even if the RPN looks small.
Step by step
- List the part, step or process you are studying.
- Write down each way it can fail.
- Write the effect of each failure.
- Score severity, occurrence and detection from 1 to 10.
- Multiply the three scores.
- Sort the list from the highest RPN to the lowest.
- Plan actions for the top items, then score again.
Why a low RPN can still be dangerous
The RPN has a weak spot. Different scores can give the same answer. A failure with S = 10, O = 1 and D = 1 gives an RPN of only 10. Another with S = 2, O = 5 and D = 1 also gives 10. Yet the first one could kill someone, and the second one is a small nuisance.
That is why many teams look at severity first, and use the RPN second. Some newer guides also use an action priority table instead of a plain RPN, which gives severity more weight. If your client or your industry uses that method, follow it.
Common mistakes
- Mixing up the detection scale, so a good control gets a high score
- Scoring alone without the people who run the machine
- Lowering severity after adding controls, when the harm is still the same
- Ignoring high-severity items because the RPN looks small
- Scoring once and never going back to review
Using RPN with other tools
RPN works well with a simple risk score. Use the risk matrix calculator for general hazards on site, and the RPN for machines and processes where detection matters. Once you add controls, the residual risk calculator helps you compare the situation before and after.
Tips for a good FMEA session
Keep the group small but mixed. An operator, a maintenance person, an engineer and a safety officer will see the process from four angles. Agree the scoring scales before you start, so everyone means the same thing by a 7. Work through the process step by step, and do not rush to the scores. Most of the value comes from the talk about how things can fail, not from the number itself.
Frequently asked questions
What does RPN stand for?
RPN stands for Risk Priority Number. It is used to rank failures in an FMEA.
What is a good RPN?
Lower is better. Many teams treat an RPN above 100 as a sign that action is needed, but the limit is your choice.
What is the highest possible RPN?
The highest RPN is 1,000, which comes from scoring 10 for severity, occurrence and detection.
Why is a high detection score bad?
Because the scale measures how hard the problem is to catch. A high score means the failure is likely to go unnoticed.
Is RPN the same as a risk score?
Not quite. A risk score uses two factors, likelihood and severity. The RPN adds a third one, detection.
Learn this properly
FMEA and risk priority numbers are covered in NEBOSH, IOSH and OSHA courses. ISH Institutes teaches these in Peshawar. Chat with us on WhatsApp and we will help you pick the right course.