WBGT calculator and estimation limits
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Shade-only WBGT approximation
— °FAdd your readings for an estimate.
No location lookup or live weather.
Not medical advice. No result is a safety clearance. Follow official local and workplace guidance.
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Not medical advice.
Not medical advice
Wet-bulb globe temperature, or WBGT, is an environmental heat-stress index used in work and sport. Unlike heat index, properly measured WBGT accounts for radiant heat and air movement as well as temperature and humidity.
Air temperature and relative humidity alone are not enough to reproduce a measured outdoor WBGT. A result based only on those inputs must be treated as a limited estimate, not a worksite reading.
Calculate from measured temperatures
The Canadian Centre for Occupational Health and Safety gives these standard equations, using temperatures in °C:
| Conditions | Equation |
|---|---|
| Direct sunlight | WBGT = 0.7*Tnwb + 0.2*Tg + 0.1*Tdb |
| Indoors or shade without direct solar load | WBGT = 0.7*Tnwb + 0.3*Tg |
Tnwb is measured natural wet-bulb temperature, Tg is black-globe temperature and Tdb is dry-bulb air temperature. A calculated psychrometric wet bulb is not automatically the same as a natural wet-bulb measurement.
Illustrative measured-input example: Tnwb = 24°C, Tg = 42°C, and Tdb = 40°C gives outdoor WBGT 0.7*24 + 0.2*42 + 0.1*40 = 29.2°C. These are example readings, not current conditions.
When globe temperature is missing
For a rough shade-only proxy, one can assume globe temperature equals air temperature and substitute an estimated wet bulb: proxy = 0.7*Tw_estimate + 0.3*Tair. That shortcut ignores actual radiant load and does not reproduce the behavior of a natural wet-bulb sensor. Wind and local conditions can make it wrong.
Label such a result “Shade-only approximation — not measured WBGT.” It is not appropriate for direct sun, hot machinery or other strong radiant heat sources. It must not be presented as a validated outdoor-WBGT estimate or used to clear a workplace or sporting activity as safe.
Use a real heat-safety assessment
OSHA recommends on-site WBGT measurement near the actual work location and consideration of workload, clothing and acclimatization. A weather-station reading or web estimate can miss local heat sources and blocked airflow.
Follow the current policy of the organization responsible for the activity. This calculator does not verify compliance with workplace rules, choose rest intervals or replace a trained heat-stress assessment.
Method and transparency
Last updated: 6 November 2026. Not medical advice.