The wet-bulb temperature is the lowest temperature evaporation can cool something to. The human body relies on sweat evaporation, so a wet-bulb temperature of 35 °C is thought to be the limit of human survival even in shade.
How to use the Wet-Bulb Temperature Calculator
- Air temperature
- Relative humidity (%)
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the air temperature and relative humidity (valid for 5–99% RH and −20 to 50 °C at sea-level pressure).
Inputs explained
| Field | What to enter |
|---|---|
| Air temperature | Units: °C, °F, K |
| Relative humidity (%) | A number |
Example values
How the main result changes when Air temperature changes and everything else stays at the example values above:
| Air temperature (°C) | Wet-bulb temperature (°C) |
|---|---|
| 15 | 9.4004 |
| 22.5 | 15.8488 |
| 30 | 22.2968 |
| 37.5 | 28.7447 |
| 45 | 35.1924 |
Formula
T_w = T·atan(0.151977·(RH + 8.313659)^{1/2}) + atan(T + RH) − atan(RH − 1.676331) + 0.00391838·RH^{3/2}·atan(0.023101·RH) − 4.686035
Worked example
Inputs — Air temperature: 30 °C; Relative humidity (%): 50.
Results — Wet-bulb temperature = 22.2968 °C; Wet-bulb depression = 7.7032 °C.
Key terms
- Wet-bulb depression
- Difference between dry- and wet-bulb temperature.
Frequently asked questions
What is wet-bulb temperature used for?
Heat stress, evaporative cooling, cooling towers and snowmaking.
How accurate is Stull's formula?
Mean absolute error under 0.3 °C in its valid range; individual errors range from about −1 to +0.65 °C.
Why is 35 °C wet-bulb deadly?
The body can no longer shed heat by sweating.
Is it the same as WBGT?
No – WBGT also includes radiation and wind.