Risk matrix calculator

Pro Site Docs · Free tool · No sign-up

Score a hazard by likelihood and severity, see where it lands on the 5 × 5 matrix, and what that band means for the RAMS.

How the 5 × 5 matrix works

Risk is scored as likelihood × severity, each on a 1-5 scale, giving a number from 1 to 25. The number is not a measurement - it is a way of comparing hazards so the ones that matter get the effort. A fall from height scores high because severity is 4 or 5 whatever the likelihood; a paper cut never gets above low however often it happens.

Raw versus residual

Score each hazard twice: once as if nothing were in place (the raw risk) and again with your controls applied (the residual risk). The gap between the two is the point of the risk assessment - it shows the controls are doing something. If the residual score is still high, the controls are not adequate, and PPE alone almost never moves a score more than one band. A good RAMS shows both numbers next to each hazard; see how to write a RAMS for the layout.

The bands are a convention, not law

The Management of Health and Safety at Work Regulations require a "suitable and sufficient" assessment; they do not require a matrix at all, let alone this one. The 5 × 5 grid and the bands used here (1-4 low, 5-9 medium, 10-15 high, 16-25 very high) are the most common convention on UK sites and match what most pre-qualification questionnaires expect. If a client's scheme uses 3 × 3 or different cut-offs, use theirs on their job.

Where people go wrong

Scoring likelihood for the whole job rather than for the specific task ("someone will fall eventually" is 5; "this person, on this step, doing this" might be 2). Scoring severity as the usual outcome rather than the reasonably foreseeable worst one. And scoring everything medium so nothing stands out - if every line says 9, the assessment is telling you nothing.

FAQs

What is a 5x5 risk matrix?

A grid that scores each hazard by likelihood (1-5) and severity (1-5), multiplied to give a rating from 1 to 25. It is used to prioritise hazards in a risk assessment and to show that controls have reduced the risk.

What risk score is acceptable?

Under the common convention, 1-4 is low and acceptable, 5-9 medium and acceptable only with controls in place, 10-15 high and needs further controls before work starts, 16-25 very high and the work should not proceed. Client schemes vary.

Is a risk matrix a legal requirement?

No. The law requires a suitable and sufficient risk assessment. A matrix is one widely accepted way of showing you have weighed likelihood and severity, but a simple high/medium/low judgement is also acceptable for straightforward work.

Should the residual risk always be low?

Not always, but it should be as low as reasonably practicable. Some construction tasks stay medium even with good controls. A residual high score means the job needs redesigning, not just more PPE.

Get the documents ready-made

Every RAMS and risk assessment in our library uses this matrix with the raw and residual columns already laid out. Start with the Risk Assessment Library or a single RAMS template for your trade.

General guidance only. This article explains how the rules generally work in UK construction. It is not advice for your specific site, task or project, and it is not legal advice. Your own risk assessment, method statement and arrangements must be prepared and checked by a competent person for the actual work being done.