What is a risk matrix?
A risk matrix combines how likely a hazardous event is with how severe the consequence would be. The product (or mapped cell) gives a priority score for risk assessment, permits, and toolbox talks.
Risk score = Likelihood × Severity. Common workplace grids are 3×3, 4×4, and 5×5. This free tool multiplies the two ratings — always follow your own risk-assessment standard when band cut-offs differ.
Risk Matrix Calculator
Risk matrix · Likelihood × Severity
Score a hazard on a 3×3, 4×4, or 5×5 matrix. Use one written rating table for your team — bands here are indicative.
Formula: Risk Score = Likelihood × Severity
- Define each L and S rating in writing before the team scores.
- High severity still needs attention even when the product looks moderate.
- Link high/extreme scores to actions, owners, and review dates.
Typical 5×5 bands (indicative)
| Score | Band | Typical action |
|---|---|---|
| 1–4 | Low | Monitor; routine controls |
| 5–9 | Medium | Specific controls and review dates |
| 10–16 | High | Senior review; strengthen controls before work |
| 17–25 | Extreme | Do not proceed until risk is reduced |
Worked examples (5×5)
- Likelihood 2 × Severity 2 = 4 (low)
- Likelihood 3 × Severity 4 = 12 (high)
- Likelihood 5 × Severity 5 = 25 (extreme)
How to use it well
- Define likelihood and severity in writing before scoring.
- Score the residual risk after planned controls, and the inherent risk if your form requires both.
- High severity with low likelihood still needs attention — do not hide behind a medium product.
- Link each high/extreme score to owners, actions, and due dates.
Risk matrix vs RPN
A risk matrix is usually two-factor (L×S). An FMEA RPN multiplies Severity × Occurrence × Detection. Use the matrix for task risk assessments; use RPN when you are ranking failure modes in an FMEA.
Frequently asked questions
Which grid size should I choose?
Use the size in your company procedure. 5×5 is common for detailed workplace risk assessments; 3×3 suits quick field assessments when your standard says so.
Are the colour bands universal?
No. Bands here are indicative. ISO 31000 leaves matrix design to the organisation. Match your risk-assessment procedure’s cut-offs.
Is Likelihood the same as probability?
In practice teams use likelihood, probability, or frequency scales. What matters is a shared written definition for each score from 1 to N.
Can two different hazards share one score?
Yes. Always read the separate likelihood and severity ratings, not only the product — especially when severity is high.
