🌡️ Wet Bulb Temperature Calculator
Enter the temperature and humidity to get the wet-bulb temperature — the true limit of how much the body can cool by sweating.
Wet-bulb temperature
79.9°F
26.6°C
Heat-stress level
Caution with activity
The wet-bulb temperature is the lowest that evaporative cooling (sweating) can reach — so a high wet-bulb means your body can't cool down. A sustained 35°C (95°F) wet-bulb is considered the limit of human survival. From Stull's (2011) formula, valid −20 to 50°C and 5–99% humidity at sea level. Not a substitute for official heat warnings. 🔒 In your browser.
How the wet bulb temperature calculator works
The wet-bulb temperature is the lowest temperature reachable by evaporating water into the air — the reading of a thermometer wrapped in a wet cloth. It sets the hard limit on how much your body can cool itself by sweating. The tool uses Stull's (2011) empirical formula, accurate from the temperature and relative humidity at normal sea-level pressure.
A sustained wet-bulb temperature of 35°C (95°F) is widely cited as the theoretical limit of human survival — at that point sweat can't cool you even at rest, whatever you do. Real danger begins well below that during exertion. Stull's formula is valid from −20 to 50°C and 5–99% humidity at sea level, and isn't a substitute for official heat-health warnings.
Frequently asked questions
What is wet-bulb temperature?
The lowest temperature achievable by evaporating water into the air — literally the reading of a wet-cloth-wrapped thermometer. It combines heat and humidity into the limit of evaporative (sweat) cooling.
Why is a 35°C wet-bulb dangerous?
At a wet-bulb temperature of 35°C (95°F), the air is so warm and humid that sweat can no longer evaporate to cool you — body temperature rises even at rest in the shade. It's regarded as the theoretical limit of human survivability.
How is wet-bulb temperature calculated?
This tool uses Stull's (2011) formula, which estimates the wet-bulb temperature from air temperature and relative humidity at sea-level pressure, accurate to within about 1°C over normal conditions.
How is wet-bulb different from the heat index?
The heat index is a "feels like" temperature scaled to human perception; the wet-bulb temperature is a physical limit of cooling. Wet-bulb is the better measure of true heat danger, especially for extreme humid heat.
What wet-bulb temperature is safe?
Below about 25°C (77°F) is generally safe; 28–31°C limits safe exertion; above 32°C is dangerous even with rest, and 35°C is the survivability limit. These thresholds shift with acclimatisation, age and health.