risk · Free · Open Source · MIT

Risk Matrix Calculator

5×5 or 4×4 risk matrix scoring. Based on ISO 45001:2018 / IEC 31010. Results shown with the full formula so you can verify. Zero signup, zero tracking, zero data sent to a server — all calculation is client-side.

Inputs

Likelihood (1-5)

Severity (1-5)

Matrix size

5×5 risk matrix · EXTREME

risk score

Intolerable — stop work, escalate to leadership

Raw JSON result

{
  "score": 20,
  "band": "extreme",
  "color": "#DC2626",
  "action": "Intolerable — stop work, escalate to leadership",
  "matrix": "5×5"
}

Overview

About the Risk Matrix Calculator

Risk matrices are the most common semi-quantitative risk scoring method in HSE. A 5×5 matrix (likelihood × severity) is standard in oil & gas (Aramco SAIC-SS, ADNOC, QatarEnergy, IOGP); a 4×4 matrix is common in construction. Both are supported.

Required by ISO 45001:2018 Clause 6.1.2 (hazard identification and risk assessment), IEC 31010 (risk management techniques), and nearly every national OSH framework. This calculator outputs the risk score, risk band (low/medium/high/extreme), recommended action, and colour-code.

Formula

Risk = Likelihood × Severity

Regulation

ISO 45001:2018 / IEC 31010

How to use

Step-by-step: using the Risk Matrix Calculator

1
Identify the hazard scenario you're scoring.
2
Score Likelihood (1-5) using your organisation's definitions.
3
Score Severity (1-5) using your organisation's definitions.
4
Read the risk score (L × S), band, and recommended action.

Worked examples

Risk Matrix Calculator — real-world examples

Hot work in a flammable atmosphere

Likelihood 4 (likely if controls fail) × Severity 5 (catastrophic — fatality possible from ignition). Score = 20 → EXTREME. Action: stop work, escalate. Re-plan with engineering controls (gas-free certificate, hot-work permit with fire watch) to reduce to Likelihood 1 × Severity 5 = 5 → MEDIUM.

Who uses this calculator

Used by safety professionals worldwide

●Risk assessment authors (JSA, HAZOP, HAZID, TRA)
●ISO 45001 implementation teams
●Oil & gas contractor HSE
●Construction HSE managers
●ALARP justification for regulator submissions

Watch out for

Common mistakes when calculating risk matrix calculator

⚠Using subjective scales without defined likelihood/severity anchors. Different people score differently without anchors.
⚠Scoring residual risk instead of raw risk. Best practice: score both (pre-controls + post-controls) and show reduction.
⚠Applying matrix blind-spots — a 1 × 5 (low likelihood, catastrophic severity) scores low (5) but warrants robust bow-tie analysis because of severity alone.

FAQ

Frequently asked questions

5×5 vs 4×4 risk matrix?+

5×5 is standard in oil & gas (Aramco, ADNOC, QatarEnergy, IOGP). 4×4 is common in construction. Use what your organisation or client specifies.

Can risk scoring alone be the HAZID output?+

No. A risk matrix ranks but doesn't identify hazards. Use HAZID / HAZOP / what-if techniques to identify, then risk matrix to rank. ISO 45001 Clause 6.1.2 requires both.

Regulation citations

Authoritative sources

ISO 45001:2018 — Occupational Health and Safety Management Systems
https://www.iso.org/standard/63787.html

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Free for any website, blog, or course — MIT / CC BY 4.0. Attribution stays visible.

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SmartQHSE is the AI-powered HSE / QHSE platform built on top of these formulas — permits-to-work, AI risk assessments, incident management, contractor prequalification, ISO 45001 compliance dashboards. Used in 40+ countries.

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