Welcome to our wet-bulb calculator, where you can work out the wet bulb temperature with just two numbers: temperature and relative humidity. Keep reading if you want to discover some wet-bulb applications, what the military benefits of the Wet-Bulb Globe Temperature, and what it has to do with our health. If you want to find out more about our atmosphere, check out our heat index calculator and our air density calculator.

What is the wet-bulb temperature?

Despite what you might think at first, wet-bulb temperature has nothing to do with light bulbs. It is instead the temperature read by a special thermometer that is wrapped in water-soaked fabric and ventilated. This thermometer is part of a device called a psychrometer. It includes a dry-bulb thermometer, a wet-bulb thermometer and a psychrometric chart - a graph that plots the relationships between the dry and wet-bulb temperature, relative humidity, and dew point at constant pressure.

By definition, wet-bulb temperature is the lowest temperature a portion of air can acquire by evaporative cooling only. When air is at its maximum (100 %) humidity, the wet-bulb temperature is equal to the normal air temperature (dry-bulb temperature). As the humidities decreases, the wet-bulb temperature becomes lowers than the normal air temperature.

Data about the wet-bulb temperature is essential when it comes to preventing our body from overheating. Our bodies sweat to cool off, but, because water evaporates slower in more humid conditions, we cool down a lot slower in humid conditions. This causes our internal body temperature to rise. If the wet-bulb temperature exceeds 35 °C (95 °F) for an extended period of time then people in the surrounding area are at risk of hyperthermia.

How to calculate the wet-bulb temperature?

Although many equations have been created over the years our calculator uses the Stull formula, which is accurate for relative humidities between 5% and 99% and temperatures between -20°C and 50°C. It loses its accuracy in situations where both moisture and heat are low in value, but even then the error range is only between -1°C to +0.65°C.

The wet-bulb calculator is based on the following formula:

Tw = T * arctan[0.151977 * (rh% + 8.313659)^(1/2)] + arctan(T + rh%) - arctan(rh% - 1.676331) + 0.00391838 *(rh%)^(3/2) * arctan(0.023101 * rh%) - 4.686035

It might look intimidating, but don't worry - we do all the calculations for you. Just input two numbers:

  • T Temperature - air temperature or dry-bulb temperature is the temperature given by a thermometer not exposed to direct sunlight.

  • rh% Relative humidity - a ratio of how much water vapor is in the air to how much it could contain at a given temperature.

If you would like to know more about the relative humidity formula, check out our dew point calculator. You can also use it to calculate the relative humidity if you know the dew point temperature. Feel free to check it out!

Wet-bulb calculator applications

The wet-bulb temperature might not be a widely known measure, but it has some valuable functions:

  • Construction - different materials react differently to different humidities, so this temperature is needed when designing a building in different climates.

  • Snowmaking - snow production needs low temperatures and when the humidity decreases the temperature rises.

  • Meteorology - forecasters use wet-bulb temperature to predict rain, snow, or freezing rain.

Wet-Bulb Globe Temperature

Wet-Bulb Globe Temperature is a kind of an apparent temperature - the temperature perceived by humans - used to estimate the effect of temperature, humidity, wind speed, and sunlight on humans. Athletes, industrial hygienists and the military use it to prevent heat stroke by following guidelines for physical activity and water intake.

Wet-Bulb Globe Temperature is determined by the following equation:

WBGT = 0.7 * Tw + 0.2 * Tg + 0.1 * T

where Tg - the globe thermometer temperature - is measured by a thermometer situated in a black globe. It allows for the estimation of direct solar radiation.

Measured indoors, without direct solar radiation/sunlight, the Wet-Bulb Globe Temperature uses a shortened formula:

WBGT = 0.7 * Tw + 0.1 * T

Wet-Bulb Globe Temperature gives us vital information if we want to be safe on warmer days.

Julia Żuławińska.

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