Wet Bulb Temperature Calculator
Find the wet-bulb temperature from air temperature and humidity, a key measure of dangerous heat.
About the Wet Bulb Temperature Calculator
The wet-bulb temperature is the lowest temperature evaporation can cool something to. Because people cool by sweating, it sets a limit on how well the body can shed heat. A wet-bulb of 35 °C was long cited as the theoretical survival limit; lab studies (Vecellio et al., 2022) suggest young healthy people reach their limit nearer 31 °C. This uses Stull's (2011) formula, accurate to about ±1 °C for 5–99% humidity at normal air pressure.
The formula
Tw = T·atan(0.151977√(RH + 8.313659)) + atan(T + RH) − atan(RH − 1.676331) + 0.00391838·RH^1.5·atan(0.023101·RH) − 4.686035
Worked example
Example: Wet-bulb temperature = 89.8 °F
- Inputs: Air temperature: 100; In: °F; Relative humidity: 66%.
- Formula: Tw = T·atan(0.151977√(RH + 8.313659)) + atan(T + RH) − atan(RH − 1.676331) + 0.00391838·RH^1.5·atan(0.023101·RH) − 4.686035
- Result: Wet-bulb temperature = 89.8 °F
Questions people ask
Is wet-bulb the same as heat index?
No. Heat index is a 'feels like' temperature; wet-bulb is a physical limit on cooling.
What about WBGT?
Wet-bulb globe temperature also includes sun and wind and is used for sport and work guidance.