environmental · Free · Open Source · MIT

WBGT Heat Stress Calculator

Wet Bulb Globe Temperature. Based on ACGIH TLV / ISO 7243. 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
WBGT heat stress · EXTREME
34°C
Work/rest: Stop work
ACGIH TLV / ISO 7243 — moderate workload, acclimatised
Raw JSON result
{
  "wbgt": 34,
  "riskLevel": "extreme",
  "acgihWorkRestRatio": "Stop work",
  "regulation": "ACGIH TLV / ISO 7243 / NIOSH Heat Stress Criteria"
}
Overview

About the WBGT Heat Stress Calculator

WBGT (Wet Bulb Globe Temperature) is the gold-standard heat stress metric — ACGIH Threshold Limit Value / ISO 7243. It combines wet-bulb (humidity + evaporation), globe (radiant heat), and dry-bulb (air temperature) into a single value that predicts heat illness risk better than any simpler measure.

Critical for GCC summer construction (UAE, Saudi Arabia, Qatar, Oman, Kuwait, Bahrain all enforce midday work bans based on WBGT), foundry and glass-making operations (indoor radiant heat), firefighter training, and agricultural work in hot climates. The calculator outputs WBGT in °C plus ACGIH TLV-based work/rest ratios for acclimatised and unacclimatised workers.

Formula
WBGT = 0.7·Tw + 0.2·Tg + 0.1·Td (outdoor with sun)
Regulation

ACGIH TLV / ISO 7243

How to use

Step-by-step: using the WBGT Heat Stress Calculator

  1. 1
    Measure (or estimate) dry-bulb temperature in °C.
  2. 2
    Measure relative humidity as a percentage.
  3. 3
    Measure globe temperature (black globe thermometer, 150mm). If not available, estimate as dry-bulb + 5°C in sun, + 2°C in shade.
  4. 4
    Select 'outdoor' if work is in direct sunlight, 'indoor' if not.
  5. 5
    Read WBGT + recommended work/rest cycle per ACGIH TLV.
Worked examples

WBGT Heat Stress Calculator — real-world examples

Dubai construction, midday July

Dry-bulb 42°C, RH 50%, globe 48°C, outdoor. WBGT ≈ 34.5°C → EXTREME. Work/rest: stop work. This is why UAE bans outdoor work 12:30-15:00 June-September.

Steel foundry, air-conditioned shop

Dry-bulb 32°C, RH 30%, globe 42°C (radiant heat from furnaces), indoor. WBGT ≈ 30°C → HIGH. Work/rest cycle: 50/50 per hour for moderate-workload acclimatised workers.

Who uses this calculator

Used by safety professionals worldwide

Watch out for

Common mistakes when calculating wbgt heat stress calculator

FAQ

Frequently asked questions

What is WBGT?+

Wet Bulb Globe Temperature — a composite heat stress metric combining air temperature, humidity, and radiant heat. Adopted by ACGIH and ISO 7243 as the gold standard.

What WBGT triggers work/rest cycles?+

For moderate-workload acclimatised workers (ACGIH TLV): continuous <27.5°C; 75/25 at 27.5-29.5; 50/50 at 29.5-31.5; 25/75 at 31.5-32.5; stop work above 32.5°C. Unacclimatised: subtract 2.5°C.

What WBGT does UAE/Saudi/Qatar midday work ban correspond to?+

GCC midday bans (12:00-15:00 roughly) align with WBGT typically 32-35°C in mid-summer. Ban is minimum compliance; WBGT-based cycling should apply outside ban hours too.

Regulation citations

Authoritative sources

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

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