5x5 Risk Matrix Explained: How to Calculate Risk Levels (UK Guide)
A 5x5 risk matrix is a simple tool used in health and safety to work out the level of risk. It multiplies the likelihood of something happening by the severity of the consequences if it does happen. This gives you a risk score (between 1-25) that shows whether the risk is low, medium, high, or very high.
What Is a 5x5 Risk Matrix?
A 5x5 risk matrix is a chart used to score risk. It has two parts:
- • Likelihood: How likely is the risk to happen?
- • Severity: How bad would it be if it did happen?
Both are scored from 1 to 5. You multiply them together to get the risk score. The higher the number, the more serious the risk.
How the 5x5 Risk Matrix Works
You score likelihood and severity separately, then multiply the two numbers:
Risk Score = Likelihood × Severity
The score tells you how urgent the risk is and what action to take.
Likelihood Ratings (1 to 5)
These ratings describe how often a hazard could cause harm:
- 1 – Rare: Highly unlikely. Almost never happens. Example: Being struck by lightning at work.
- 2 – Unlikely: Could happen, but not expected. Example: A tool breaking during normal use.
- 3 – Possible: May happen at some point. Example: Slipping on a wet floor if it's not cleaned often.
- 4 – Likely: Expected to happen regularly. Example: Cuts from handling sharp materials without gloves.
- 5 – Almost Certain: Will probably happen soon or often. Example: Eye injuries from grinding without goggles.
Severity Ratings (1 to 5)
These ratings describe how bad the outcome could be:
- 1 – Negligible: Very minor harm. No treatment needed. Example: A small scratch.
- 2 – Minor: Small injury. May need first aid. Example: A bruise or small cut.
- 3 – Moderate: Injury that may need medical treatment. Example: Sprained ankle, burn.
- 4 – Major: Serious injury. Likely to need hospital treatment or time off work. Example: Broken bone, deep laceration.
- 5 – Catastrophic: Death or life-changing injury. Example: Fatality, permanent disability.
How to Calculate the Risk Score
Follow these simple steps:
- 1. Look at the hazard and decide how likely it is to cause harm. Pick a number from 1 to 5.
- 2. Decide how serious the harm would be. Pick a number from 1 to 5.
- 3. Multiply the two numbers together.
- 4. Use the risk score to decide what action to take.
Example Calculation
Let's say you're assessing the risk of someone slipping on a wet floor:
- • Likelihood: 3 (Possible – floors get wet sometimes)
- • Severity: 3 (Moderate – could sprain ankle or worse)
Risk Score = 3 × 3 = 9
This is a medium risk. You should put control measures in place (like wet floor signs and non-slip mats).
Understanding the Risk Score
Once you have your score, you need to know what it means. Here's a common breakdown used in UK risk assessments:
- 1–4: Low Risk – Acceptable. No urgent action needed, but keep it under review.
- 5–12: Medium Risk – Control measures should be put in place to reduce the risk.
- 13–20: High Risk – Action needed urgently. Don't start work until the risk is reduced.
- 21–25: Very High Risk – Stop work immediately. Risk must be eliminated or reduced before continuing.
When to Use a 5x5 Risk Matrix
5x5 risk matrices are widely used in:
- • Risk assessments (RAMS documents)
- • COSHH assessments (chemical risks)
- • Manual handling assessments
- • Construction site safety reviews
- • Pre-task safety planning
It's especially useful for businesses that need to comply with UK health and safety laws (like the Health and Safety at Work Act 1974).
Benefits of Using a 5x5 Risk Matrix
- ✓ Simple and visual: Easy for anyone to understand, even without training.
- ✓ Quick to use: Helps you make fast decisions about risk.
- ✓ Consistent: Everyone uses the same scoring system, so assessments are fair.
- ✓ Prioritises action: Helps you focus on the most dangerous risks first.
- ✓ Meets UK legal standards: Widely accepted by HSE and CHAS auditors.
Common Mistakes to Avoid
- ✗ Guessing the scores: Always base your ratings on real observations and evidence.
- ✗ Scoring too low: Don't downplay risks just to avoid extra work.
- ✗ Not reviewing scores: Risks change over time – review your matrix regularly.
- ✗ Ignoring control measures: The matrix is only useful if you act on the results.
Frequently Asked Questions
What does 5x5 mean in a risk matrix?
It means there are 5 levels of likelihood and 5 levels of severity. When you multiply them, you get a score between 1 and 25.
Is a 5x5 risk matrix required by law in the UK?
No, but you are legally required to assess risks under the Management of Health and Safety at Work Regulations 1999. A 5x5 matrix is a recognised way to do this.
Can I use a different risk matrix?
Yes. Some organisations use 3x3 or 4x4 matrices. As long as your method is clear and consistent, it's acceptable. The 5x5 is popular because it gives more detail.
What's the difference between likelihood and severity?
Likelihood = how often it could happen. Severity = how bad it would be if it did. You need both to get the full picture of the risk.
Do I need to include a 5x5 matrix in my RAMS?
It's not mandatory, but many principal contractors and clients expect to see risk scores in your RAMS documents. Including it shows you've properly assessed the risk.
What if I get different scores from different people?
This can happen. Discuss the differences as a team and agree on the most accurate score. It's better to be cautious and score higher if in doubt.
Final Thoughts
A 5x5 risk matrix is a simple, effective tool for assessing risk. It helps you make informed decisions, prioritise safety, and meet your legal duties.
Whether you're writing a risk assessment for a construction site, handling chemicals, or planning manual handling tasks, the 5x5 matrix gives you a clear way to score and manage risk.
If you need help creating professional RAMS documents with built-in risk matrices, RiskGen can help. Our platform makes it easy to assess risks, score them properly, and produce compliant health and safety documentation in minutes.
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