Wet bulb temperature calculator
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Wet-bulb temperature
— °FAdd your readings for an estimate.
No location lookup or live weather.
Not medical advice. No result is a safety clearance. Follow official local and workplace guidance.
Your calculation record
Not medical advice.
Not medical advice
Wet-bulb temperature describes the cooling possible through evaporation under specified conditions. A wet-bulb thermometer uses a wetted sensor; evaporation cools the sensor. In humid air, less evaporative cooling is available.
The estimate here uses air temperature and relative humidity. It is not a measurement of your body temperature, a personal tolerance limit or a reading from a natural wet-bulb sensor used in WBGT equipment.
What is wet-bulb temperature?
Wet bulb describes evaporative cooling, not dew point or WBGT.
Read the short wet-bulb guide for a worked example, comparison cards and assumptions.
Stull's approximation
Roland Stull's 2011 paper provides an empirical approximation at standard sea-level pressure, 101.325 kPa. With T in °C, R as relative humidity in percent, and arctangents evaluated in radians:
Tw = T*atan(0.151977*sqrt(R + 8.313659))
+ atan(T + R) - atan(R - 1.676331)
+ 0.00391838*R^(3/2)*atan(0.023101*R)
- 4.686035
The paper describes a range of −20 to 50°C and 5–99% RH, excluding combinations of cold temperatures and low humidity. Pressure is fixed in this approximation; altitude is not accounted for. See also UCAR's method documentation.
Published method example: 20°C and 50% relative humidity gives approximately 13.7°C. This is a useful arithmetic check, not a claim that an inexpensive humidity sensor is accurate to a tenth of a degree.
Do not turn wet bulb into a survival timer
An environmental reading cannot tell you how long a person can remain in the heat. Exertion, sunlight, clothing, age, health and acclimatization all matter. Do not wait for a particular wet-bulb threshold before responding to symptoms.
For active workplaces, consult OSHA's heat hazard guidance and the WBGT explanation. For warning signs and emergency information, see the heat FAQ.
Method and transparency
Last updated: 6 November 2026. Not medical advice.