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Wet-bulb temperature
Now
—°C
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- Air temp
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- Humidity
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- Feels like
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Hour by hour · two days back, seven ahead
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The scale
Wet-bulb temperature is the lowest temperature your skin can reach by sweating. The bands below assume shade and a breeze — full summer sun can push conditions roughly one band worse.
What is wet-bulb temperature?
It’s the reading a thermometer gives when its bulb is wrapped in wet cloth and ventilated — in other words, the coolest your body can get by evaporating sweat. Air temperature tells you how hot it is; wet-bulb temperature tells you whether sweating still works. Dry heat at 40 °C can be safer than humid heat at 30 °C, and this single number is why.
At a wet-bulb reading of 35 °C, evaporation stops cooling you entirely — the theoretical limit of human survival, fatal within hours even resting in shade. Laboratory work at Penn State (the 2022 PSU H.E.A.T. project) found that for young, healthy adults the practical limit is closer to 31 °C. Long before either point, exercise becomes dangerous: most heat casualties happen at readings in the mid-20s, not the 30s.
Forecast values are for 2 m above ground in shade. Direct sun, still air, dark clothing and pavement all add heat stress on top of what this page shows. Guidance here is general information, not medical advice.