WBGT vs heat index

Two heat numbers that answer different questions.

Heat index

The heat index combines air temperature and humidity into a "feels like" temperature in the shade with light wind. It's easy to understand, and NWS heat advisories use it.

Wet-bulb globe temperature

WBGT combines a natural wet-bulb reading (humidity and wind), a black-globe reading (sun and radiant heat) and air temperature. Because it includes sun and wind, it's the measure NIOSH's work/rest limits are based on.

Why it matters

On a sunny, breezy day and a cloudy, still day with the same heat index, workers face different heat stress. WBGT captures that difference. The heat index doesn't.

Where to get WBGT

The National Weather Service publishes an hourly WBGT forecast for much of the country. Aeonis Heat reads it for your site and turns it into a work/rest plan.