Risk Matrix Calculator (5x5): Likelihood x Consequence
Rate a risk on a standard 5x5 matrix, then see how much your planned controls lower it.
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How this calculator works
A risk matrix ranks a risk by two things: how likely it is that someone is harmed, and how bad the harm could be. Each is rated from 1 to 5 and the two numbers are multiplied to give a score from 1 to 25, which falls in a band from low to extreme.
The calculator lets you rate the risk as it is now, then again after the controls you plan to add. A control that does not lower the likelihood or the consequence does not lower the score, which is a useful check on whether a control really does anything.
The score is only a way to compare and rank risks and to show your reasoning. The law asks you to eliminate a risk, or if that is not reasonably practicable to minimise it, whatever its score, and to work down the hierarchy of control: eliminate, substitute, isolate or engineering controls, administrative controls, and protective equipment last.
Formulas used
- S = L \times C
- S_{after} = L_2 \times C_2
- \text{reduction} = (S_1 - S_2)/S_1
Worked example
With the default numbers in the calculator above:
- Likelihood of harm now: 3 Possible
- Worst credible consequence now: 4 Major (permanent disability or life-changing injury)
- Risk score now: 12
- Band now (example bands): High
Change the numbers in the calculator to see the full working, every step, for your own case.
Common questions
Is a low score safe?
No. A low score only says the risk ranks low compared with others. The duty is still to eliminate or minimise the risk so far as is reasonably practicable.
Are these bands the official ones?
No. They are a common example. Many businesses set their own bands and descriptors in their risk management procedure: use yours if you have one.
Which consequence should I rate?
The worst credible consequence, not the most likely one. A fall from height is rated for a serious injury or death, even if most falls end in a bruise.
Related calculators
Further reading: How to manage work health and safety risks Code of Practice (Queensland); Safe Work Australia guidance on managing risks; ISO 31000 (the standard itself is licensed).
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