5×5 risk matrix calculator

How the 5×5 risk matrix works

Each hazard gets two scores from 1 to 5:

• Likelihood: how likely is it that harm will happen? From 1 (rare) to 5 (almost certain).
• Severity: how bad would it be? From 1 (minor, first aid) to 5 (fatal).

Multiply them to get a risk rating from 1 to 25. Score the risk before your controls, add controls, then score it again. The second score is the residual risk.

A common banding: 1–4 low, 5–9 medium, 10–16 high (stop and add controls), 17–25 very high (do not start). Tap any square in the calculator above to see what it means.

Using the matrix properly

• Controls lower likelihood far more often than severity. A fall from a roof is still potentially fatal; edge protection makes it much less likely.
• Don't let the number replace judgement. A score of 10 for silica dust and a score of 10 for a paper cut aren't the same, because severity 5 outcomes need more attention.
• Be consistent. Use the same scales across all your RAMS so clients can compare them.
• Act on high scores. Anything still high after controls means changing the method, not adding more PPE.

3×3 vs 5×5 risk matrix

A 3×3 matrix (low, medium, high) is simpler and fine for low-risk work. A 5×5 matrix gives more resolution, which main contractors on larger sites usually expect. Use whichever your clients ask for, and use it consistently.

Worked example: cutting blocks with a disc cutter

Notice that the silica score stays medium even with good controls, because the harm is severe. That's a prompt to look for a better method, such as ordering blocks cut to size or using a block splitter.

Frequently asked questions