Risk Assessment Matrix Calculator
Quick answer
Risk score equals likelihood × severity. On a 5×5 matrix the result runs from 1 to 25: 1–4 low, 5–9 medium, 10–15 high and 16–25 very high, requiring immediate action.
Risk score
Likelihood × severity on a 5×5 matrix.
Risk score
9
out of 25
1–4 low: monitor · 5–9 medium: plan controls · 10–15 high: controls before work continues · 16–25 very high: stop work.
The risk matrix is the most widely used tool in occupational safety because it converts an argument into a number. Two people who disagree about whether a hazard is "serious" can usually agree on how likely it is and how badly it would hurt someone, and the matrix does the rest.
Its weakness is the same as its strength. The score is only as good as the two judgements behind it, and a matrix filled in to justify a decision already made is worse than no matrix at all.
What the two axes mean
Likelihood runs from 1, meaning it would be rare over the life of the activity, to 5, meaning it is expected to happen regularly. Judge it for the task as actually performed, including shortcuts people really take, not the written procedure.
Severity runs from 1, a minor injury needing no treatment, to 5, a fatality or permanent disability. Rate the credible worst outcome rather than the most likely one — a fall from height is a 5 even when most falls cause bruises.
Score bands and what each demands
A score of 1 to 4 is low: monitor and record it, no immediate action required. Five to 9 is medium: plan controls and set a deadline. Ten to 15 is high: controls must be in place before the work continues.
Sixteen to 25 is very high. Work stops until the risk is reduced. The hierarchy of control applies in order — eliminate the hazard, substitute something safer, engineer a barrier, change the procedure, and only then rely on personal protective equipment, which protects one person and only when worn correctly.
Rescoring after controls
The point of the exercise is the residual score. Assess the hazard as it stands, apply controls, then score it again with those controls assumed in place — that second number is what the assessment is actually for.
Controls almost always reduce likelihood rather than severity. A guardrail does not make a fall less harmful; it makes the fall less likely. Severity usually only drops when the hazard itself is eliminated or substituted.
Frequently asked questions
- Should I score the worst case or the likely case?
- Score the credible worst outcome for severity and realistic frequency for likelihood. Scoring the likely outcome on both axes systematically understates hazards that are rare but catastrophic.
- What score means work must stop?
- On a 5×5 matrix, 16 and above is normally treated as intolerable: the activity does not proceed until controls bring the residual score down.
- Is a 5×5 matrix better than 3×3?
- It gives finer separation between hazards, which helps when prioritising a long list. A 3×3 is quicker and adequate for simple, low-variety work.
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Updated 2026-09-20 · all calculators. Results are estimates for guidance, not professional advice.