How is the risk rating calculated?

Risk rating equals likelihood multiplied by severity. On a 5×5 matrix each runs 1 to 5, giving scores from 1 to 25; on a 3×3 matrix each runs 1 to 3, giving 1 to 9. The product is then placed into a colour band that sets the priority for action.

What do the bands mean on a 5×5 matrix?

A common HSE-style banding is: 1–4 low (acceptable, monitor), 5–9 medium (act within a defined period), 10–15 high (act soon, additional controls needed), and 16–25 intolerable (stop the activity until risk is reduced). Your organisation's risk appetite may set slightly different cut-offs.

What is the hierarchy of controls?

It is the ranked order of control effectiveness: eliminate the hazard, substitute it for something safer, apply engineering controls (guards, ventilation), apply administrative controls (procedures, training), and lastly personal protective equipment (PPE). Higher tiers are always preferred because they do not rely on human behaviour.

Why is PPE the last resort?

PPE only protects the individual wearing it, can fail or be worn incorrectly, and does nothing to reduce the hazard itself. It is the least reliable control, so it should supplement higher-tier measures rather than be the primary safeguard for a significant risk.

Does a low rating mean no action is needed?

Not necessarily. A low rating means the residual risk is broadly acceptable, but you should still record the assessment, keep existing controls in place, and review it periodically or after any incident, change of process, or new information.

Health & Safety Risk Matrix Calculator

A risk matrix turns two judgements — how likely harm is and how serious it would be — into a single rating that drives action priority. This calculator implements the standard UK HSE-style 5×5 and 3×3 matrices and then points you to the level of control the hierarchy of controls expects for that rating.

How it works

The core formula is simply the product of the two scores:

risk rating = likelihood × severity

On a 5×5 matrix this gives 1 to 25; on a 3×3 matrix it gives 1 to 9. The product is banded into low, medium, high, and intolerable. Higher bands demand controls from higher up the hierarchy:

Eliminate -> Substitute -> Engineering -> Administrative -> PPE
(most effective)                                  (least effective)

Notes and example

A task with likelihood 4 (“likely”) and severity 5 (“fatal/major injury”) on a 5×5 matrix scores 20 — intolerable. That demands stopping the activity and designing out the hazard (elimination or substitution), not just issuing PPE. The same hazard reduced to likelihood 2 after engineering controls scores 10 — high but workable with monitoring. Record every assessment and re-rate it whenever the process, people, or equipment change.