Wet Bulb Temperature Calculator — Calculate Wet-Bulb Temperature from Humidity

What is the Wet-Bulb Temperature?

The wet-bulb temperature is the lowest temperature that air can reach through evaporative cooling only. It is measured using a thermometer wrapped in water-soaked fabric (a wet wick) that is ventilated. As water evaporates from the wick, it cools the thermometer below the ambient (dry-bulb) air temperature. When humidity is 100%, no evaporation occurs and wet-bulb temperature equals dry-bulb temperature.

How to Calculate the Wet-Bulb Temperature?

Our calculator uses the Stull formula (2011), which provides excellent accuracy for relative humidities between 5% and 99% and temperatures between −20°C and 50°C:

T_w = T·arctan(0.151977·√(RH+8.313659)) + 0.00391838·√(RH³)·arctan(0.023101·RH) − arctan(RH−1.676331) + arctan(T+RH) − 4.686035

Where T is the dry-bulb temperature in °C and RH is the relative humidity in %.

Both metric (°C) and imperial (°F) unit systems are supported. Simply select your preferred unit system, enter the air temperature and relative humidity, and get the wet-bulb temperature instantly.

Wet-Bulb Calculator Applications

• Construction — Materials react differently to humidity. Wet-bulb temperature guides climate-specific building design.
• Snowmaking — Snow guns require low temperatures. As humidity drops, wet-bulb temperature rises, affecting snow production.
• Meteorology — Forecasters use wet-bulb temperature to predict rain, snow, sleet, and freezing rain.
• Agriculture — Helps assess crop stress and irrigation needs during heat events.
• Industrial hygiene — Workplace safety standards often reference wet-bulb temperature for heat stress management.

Wet-Bulb Globe Temperature (WBGT)

The Wet-Bulb Globe Temperature (WBGT) is a composite index used by the military, athletes, and industrial hygienists to assess heat stress risk. Unlike the simple wet-bulb temperature, WBGT also accounts for wind speed, radiant heat (sunlight), and air temperature:

WBGT (outdoors) = 0.7·T_w + 0.2·T_g + 0.1·T_d

Where T_w = wet-bulb temperature, T_g = globe thermometer temperature (radiant heat), T_d = dry-bulb temperature.

Why Does Wet-Bulb Temperature Matter for Human Health?

Our bodies cool themselves through sweat evaporation. In humid conditions, sweat evaporates slower, reducing our ability to cool down. When wet-bulb temperature reaches 35°C (95°F), even a healthy person at rest cannot maintain a stable core temperature — this is considered the physiological limit of human survivability.

FAQs

What is the difference between dry-bulb and wet-bulb temperature?

Dry-bulb temperature is the standard air temperature. Wet-bulb temperature is always equal to or lower than dry-bulb, and reflects the cooling effect of evaporation.

Can wet-bulb temperature exceed dry-bulb temperature?

No. Wet-bulb temperature is always ≤ dry-bulb temperature. They are equal only when relative humidity is 100%.

What is a dangerous wet-bulb temperature?

A wet-bulb temperature above 28°C is dangerous for outdoor physical activity. Above 35°C is considered fatal for extended exposure.

Does the Stull formula work for all conditions?

The Stull formula is accurate for RH between 5%–99% and temperatures between −20°C and 50°C. Outside these ranges, use a psychrometric chart.