Risk matrix calculator
The risk matrix calculator takes a likelihood score from 1 to 5 and a severity score from 1 to 5 and multiplies them to give a risk rating between 1 and 25. It uses one common scoring approach, and the scheme your employer uses may differ. The calculator helps you practise the idea of rating a risk. It does not replace a real risk assessment of a real task.
This site is independent and is not affiliated with CSCS, CITB or HSE. The calculator is a learning aid and not an official method.
Key takeaways
- A hazard is something with the potential to cause harm, and a risk is the chance that someone is harmed, together with how serious the harm could be.
- A 5 by 5 matrix scores likelihood and severity from 1 to 5, and multiplies them to give a rating from 1 to 25.
- The scoring scheme is one common approach, and the employer chooses the method used on their sites.
- A higher rating means the risk needs more control, but the number itself does not make anything safe.
- The point of rating a risk is to decide what to do about it, not to produce a score.
Hazard and risk: the concept behind the matrix
The matrix only makes sense once you are clear on two words that people often mix up. HSE's risk assessment guidance asks you to identify what may cause harm (the hazards), then decide how likely it is that someone could be harmed and how seriously (the risk).
A wet floor is a hazard. The risk depends on how many people walk across it, how likely they are to slip and how badly they could be hurt. Our hazard versus risk explainer goes through this with examples.
HSE's risk page sets out three steps: identify hazards, decide how likely harm is and how serious, and take action to eliminate or control the risk. A risk matrix sits inside the second of those steps. It gives you a structured way to compare risks so that you deal with the most serious first.
How the calculator works
You choose two scores and the calculator multiplies them.
Likelihood
Likelihood is how probable it is that the harm will happen. On the common 1 to 5 scale, 1 is very unlikely and 5 is very likely or almost certain. Base the score on what really happens: how often the task is done, how many people are exposed and what controls already exist.
Severity
Severity is how serious the harm would be if it happened. On the same scale, 1 is minor, such as a small scratch that needs no treatment, and 5 is the most serious outcome, such as a fatality or life-changing injury. Score the realistic worst outcome, not the best.
The rating
Rating = likelihood multiplied by severity. A likelihood of 2 and a severity of 3 gives a rating of 6. A likelihood of 4 and a severity of 5 gives a rating of 20. The result always falls between 1 and 25.
The 5 by 5 grid
This is the full set of products from the multiplication. Read across for likelihood, down for severity.
| Severity \ Likelihood | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| 1 | 1 | 2 | 3 | 4 | 5 |
| 2 | 2 | 4 | 6 | 8 | 10 |
| 3 | 3 | 6 | 9 | 12 | 15 |
| 4 | 4 | 8 | 12 | 16 | 20 |
| 5 | 5 | 10 | 15 | 20 | 25 |
Notice that the same rating can come from different combinations. A rating of 5 could be a risk that is very likely but trivial (5 by 1) or one that is extremely rare but catastrophic (1 by 5). Those need very different responses, which is the main weakness of any matrix. Always look at the two scores as well as the product.
What the bands mean
Many organisations group the ratings into bands such as low, medium and high, and attach an action to each band. There is no single national set of bands, so the cut-off points differ from one employer to the next. One site might treat anything above a certain number as unacceptable until further controls are in place, and another might use a different line.
Because the scheme is the employer's choice, the calculator does not tell you that a particular number is safe or unsafe. It shows you the score. Your employer's risk assessment procedure tells you what to do with it. If you are asked to use a matrix at work, use the one your employer gives you.
Using the calculator, step by step
- Pick one specific hazard, such as a trailing cable across a walkway.
- Decide who could be harmed and how. Workers, visitors and the public can all be affected.
- Score the likelihood from 1 to 5, thinking about the controls already in place.
- Score the severity from 1 to 5, thinking about the realistic worst outcome.
- Read the rating and compare it with other hazards you have scored.
- Decide what controls would reduce the risk, then score again with those controls in place.
The second scoring is the most useful part. Comparing the rating before and after a control, such as tidying the cable away or adding a cable cover, shows you whether the control makes a real difference. For more on how this fits into a full assessment, see our guide to risk assessment on site.
Checklist: is your risk rating sensible?
- [ ] I scored a single, clearly described hazard, not a vague area.
- [ ] I thought about everyone who could be harmed, not just myself.
- [ ] I scored the realistic worst outcome for severity.
- [ ] I considered the controls already in place when scoring likelihood.
- [ ] I looked at likelihood and severity separately, not only the product.
- [ ] I decided on an action, and I will check it again later.
Limits of any risk matrix
A matrix gives a rough comparison, not a measurement. Two people can score the same task differently, and neither is necessarily wrong. The numbers look precise, but they come from judgement. A matrix also cannot capture a risk that nobody has thought of, so it does not remove the need to look at the work as it is actually done, and to talk to the people doing it.
The matrix is also not the law. Employers have a duty to assess the risks to their workers and others. The matrix is one tool that can help, and HSE's Risk assessment page is the place to read the official guidance. If you are preparing for a CITB test, the useful lesson is the reasoning: identify the hazard, judge how likely and how serious, then control it. You can test your understanding with our free practice questions.
Worked example: a trailing cable on a walkway
Imagine a site where a powered hand tool is fed by a long cable that crosses a walkway used by several trades. The scores below are illustrative and come from judgement, not from any measurement.
Start with the likelihood. Many people use the walkway every day, the cable lies at floor level and nothing marks it, so a trip is quite probable. Score the likelihood 4. Now the severity. A trip on level ground is usually a minor injury, but the walkway runs beside a step down and people carry loads, so a fall could cause a broken bone. Score the severity 3. The rating is 4 multiplied by 3, which is 12.
Next, decide on controls. The best option is to remove the hazard, for example by moving the power point closer to the work so that the cable no longer crosses the walkway (general practice). If the cable has to stay, raise it clear of the floor or cover it, and keep the route tidy. With the cable out of the walking line, the likelihood drops to 2. The severity stays at 3, because a fall near a step would still be the realistic worst outcome. The new rating is 6.
What the example shows:
- The control changed the likelihood, not the severity, so the rating halved.
- The severity score is a reminder of why the step down matters, and it may justify extra controls there, such as keeping the route clear.
- The score of 6 does not mean the risk is gone. It means the risk is lower than before, and someone still needs to check the cable cover and the walkway as work goes on.
Now compare a second hazard that also scores low on paper, such as small offcuts of timber left near a bin. A likelihood of 5 and a severity of 1 gives a rating of 5. That looks similar to a rare but serious event scored 1 by 5, but the response is different: the first needs better housekeeping, and the second needs careful planning of the task. This is why you should look at both scores.
How the calculator fits with the other guides
The calculator is one small piece of a bigger picture, and our other guides fill in the rest. If you are not yet sure about the vocabulary, start with the hazard versus risk explainer. It sets out the difference between the thing that can cause harm and the chance that it will, which is the idea every score depends on.
When you are ready to see how scoring sits inside a real assessment, read our guide to risk assessment on site. It looks at the wider process of assessing a task, and the matrix helps with only one step of that process.
A sensible order for using the guides is:
- Learn what a hazard and a risk are.
- Practise scoring with the calculator on everyday examples, such as the cable above.
- Read how a full assessment is carried out and recorded.
- Check HSE's Risk assessment page for the official approach.
If you are preparing for a CITB test, the reasoning matters more than the numbers, so try the same steps on a scenario from the free practice questions and explain your choice in a sentence.
FAQ
What is a risk matrix?
A risk matrix is a grid that combines the likelihood of harm with its severity to give a risk rating. In the 5 by 5 version used here, each is scored from 1 to 5 and the two scores are multiplied. The result helps you compare risks and decide which to deal with first.
Is a score of 25 always worse than a score of 12?
Usually, but not always. A score of 25 means very likely and most serious, so it needs urgent attention. However, you should still look at the two scores, as a risk with a low likelihood and a very serious severity can need careful control even when the product looks modest.
Which scoring scheme should I use at work?
Use the scheme your employer provides. The 5 by 5 multiplication here is one common approach, but the employer chooses the method and the bands used on their sites. If you are unsure, ask your supervisor or safety adviser.
Can the calculator replace a real risk assessment?
No. It is a learning tool for practising how to rate a risk. A real assessment looks at the actual work, the people involved and the controls, and it is recorded and reviewed. Read HSE's risk assessment guidance for the official approach.
Sources
Independent guide, not affiliated with, authorised by, approved by or endorsed by CSCS or CITB. Last updated 2026-10-08.