Wet-bulb temperature is the lowest temperature a parcel of air can reach by evaporating water into it. In plain terms, it is how cool sweating can make you, and when it climbs, the body's main cooling system starts to fail.
Last updated July 9, 2026 · Live data refreshes every 15 min
The thermometer with a wet sock
Wrap a wet cloth around a thermometer's bulb and blow air across it. Evaporation pulls heat away and the reading drops below the ordinary (dry-bulb) air temperature. How far it drops depends on humidity: in dry air, lots of water evaporates and the wet-bulb reads much lower; in saturated air, nothing evaporates and the wet-bulb equals the air temperature. That gap is precisely the room your body has to cool itself by sweating.
Why it matters in the tropics
The U.S. Virgin Islands are humid, so the wet-bulb temperature sits close to the air temperature and there is little evaporative headroom. That is why a Caribbean 88°F can stress a body far more than a desert 100°F. Wet-bulb temperature is the single largest ingredient in WBGT, it carries 70% of the outdoor weighting, because it captures this evaporation limit directly.
Frequently asked questions
What is a dangerous wet-bulb temperature?
A sustained wet-bulb temperature around 95°F (35°C) is widely cited as the theoretical survivability limit, because the body can no longer shed heat by any means. Real harm begins well below that, prolonged exposure in the high-80s°F wet-bulb is already dangerous for exertion.
Is wet-bulb temperature the same as WBGT?
No. Wet-bulb temperature is a single measurement (the evaporation-limited temperature). WBGT is a composite index that combines a natural wet-bulb temperature with a globe temperature and the air temperature. Wet-bulb is the largest ingredient in WBGT, not the whole recipe.