Wet Bulb Calculator
Use our wet bulb calculator to estimate wet-bulb temperature (°F) from air temperature and relative humidity. Includes wet bulb explained, the wet bulb formula (approximation), and how to measure wet bulb temperature.
Wet Bulb Explained
Wet-bulb temperature is the temperature a thermometer would read if its bulb were covered with a wet wick and air were moved across it. Because evaporation cools the bulb, wet-bulb temperature is usually lower than the regular air temperature (dry-bulb temperature), unless the air is fully saturated.
If you want to calculate wet bulb, you need two main inputs: air temperature and relative humidity. Wet bulb is used in weather, HVAC, and heat-stress planning because it reflects how effectively sweat (evaporation) can cool the body.
Wet-bulb temperature is measured with a sling psychrometer or a ventilated psychrometer (or estimated using formulas and psychrometric relationships). This calculator provides an estimate based on temperature and relative humidity.
Wet Bulb Formula
This calculator estimates wet-bulb temperature using a widely used approximation. The approximation is typically applied in Celsius, then converted back to Fahrenheit.
Use T in °C and RH as a percent (0–100).
Convert your input temperature to °C before applying the approximation.
Convert the estimated wet-bulb value back to °F.
With hot air and moderate humidity, wet-bulb temperature stays fairly high because evaporation is limited.
Lower humidity increases evaporative cooling, so wet-bulb temperature drops more below dry-bulb temperature.
How to Find Wet Bulb Temperature
- 1
Enter the air temperature (°F). This is the dry-bulb temperature measured in the shade.
- 2
Enter the relative humidity (%).
- 3
The calculator estimates the wet-bulb temperature (°F) from temperature and humidity.
- 4
Use the result to compare conditions, especially when evaluating heat stress risk or evaporation potential.
Frequently Asked Questions
Wet-bulb temperature is measured using a thermometer with a wet wick over the bulb while air flows across it (for example, with a sling psychrometer or ventilated psychrometer). Evaporation cools the bulb, producing the wet-bulb reading.
Dry-bulb temperature is the regular air temperature. Wet-bulb temperature accounts for evaporative cooling, so it reflects both temperature and humidity and is usually lower than dry-bulb temperature unless humidity is 100%.
No. Wet-bulb temperature is not a fixed conversion from dry-bulb temperature. You need at least humidity (and for higher accuracy, pressure/altitude) because evaporation depends on the moisture content of the air.
WBGT is a different heat-stress index that can include natural wet-bulb temperature, globe temperature (radiant heat), and dry-bulb temperature. This calculator estimates wet-bulb temperature only, not WBGT.
Wet-bulb temperature indicates how effectively evaporation can cool surfaces and the human body. Higher wet-bulb values mean less evaporative cooling and higher heat stress risk.