Risk Matrix Calculator

What is a Risk Matrix?

A risk matrix is a visual tool used in workplace health and safety (WHS) risk assessment to combine two dimensions of a risk scenario: the likelihood (or probability) that a harmful event will occur, and the consequence (or severity) of harm if it does occur. By multiplying these two indices, the matrix produces a risk score that maps to a risk band — Low, Medium, High, or Extreme — each with corresponding recommended management actions and timeframes.

Risk matrices are used across virtually every industry: construction, mining, healthcare, manufacturing, oil and gas, infrastructure, and corporate environments. They are embedded in AS/NZS ISO 31000:2018 (Risk Management Guidelines), the model WHS Regulations, and thousands of safety management systems worldwide.

5×5 Risk Matrix Descriptors

The 5×5 matrix provides the finest granularity and is most appropriate for formal WHS risk assessments:

• Likelihood: 1 = Rare, 2 = Unlikely, 3 = Possible, 4 = Likely, 5 = Almost Certain
• Consequence: 1 = Insignificant, 2 = Minor, 3 = Moderate, 4 = Major, 5 = Catastrophic

Risk bands for 5×5: Scores 1–3 = Low (Green); 4–6 = Medium (Yellow); 8–12 = High (Orange); 15–25 = Extreme (Red). Note that certain score combinations (e.g., score 7) may straddle bands — the matrix assigns these based on the closest band threshold.

Risk Band Actions and Timeframes

• Low: Manage by routine procedures. No additional treatment required. Periodic monitoring.
• Medium: Designate responsibility and implement additional controls. Review within one month.
• High: Senior management attention required. Implement urgent additional controls. Act within one week.
• Extreme: Stop or suspend the activity if possible. Immediate action required before work proceeds. Notify senior management and regulator if applicable.

How to Use This Calculator

• Select the matrix size (3×3, 4×4, or 5×5) appropriate for your assessment
• Use the dropdown selectors or click directly on the matrix grid to select likelihood and consequence
• Read the risk score, band, colour, and recommended action
• Optionally enable residual risk to compare initial vs post-control risk levels

Residual Risk Assessment

After identifying the initial (inherent) risk level, the next step in the risk management process is to identify and implement controls following the hierarchy: elimination, substitution, engineering controls, administrative controls, then PPE. Once controls are in place, reassess the risk using the residual likelihood and residual consequence to confirm the risk has been reduced to an acceptable level (typically Low or Medium for most tasks).

Limitations of Qualitative Risk Assessment

Qualitative risk matrices provide a structured, rapid assessment tool but have inherent limitations. Research has shown that different assessors often assign very different likelihood and consequence ratings to identical scenarios. Risk scores should not be aggregated across different hazard types (a score of 12 from a minor health hazard does not equal a score of 12 from a catastrophic safety risk). For major hazard facilities, critical infrastructure, and high-consequence environments, quantitative risk assessment (QRA) techniques such as fault tree analysis, bow-tie analysis, and probabilistic risk assessment are required.