Last updated:

Wet Bulb Calculator

What is the wet-bulb temperature?How to calculate the wet-bulb temperature?Wet-bulb calculator applicationsWet-Bulb Globe TemperatureFAQs

With many countries reported their highest ever temperatures, such as reaching 49.6 C, it's important that you understand the different factors affecting heat and the body's ability to regulate it. What many people might fail to take into account is the combined result of the heat and humidity - the wet bulb effect. This tool will teach you about the wet bulb, and lets you estimate it's scale.

The wet bulb calculator operates on a simple principle. You can use it to work out the wet bulb temperature from 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 are, and what it has to do with our health - especially within the context of our scorching summers!

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 humidity decreases, the wet-bulb temperature becomes lower 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:

\scriptsize \begin{align*} T_\mathrm w & = T\arctan(0.151977\sqrt{RH + 8.313659}) \\ & + 0.00391838\sqrt{RH^3}\arctan(0.023101RH) \\ & - \arctan(RH - 1.676331) \\ & + \arctan(T + RH) \\ & - 4.686035 \end{align*}

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

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

• $\footnotesize RH [\%]$ — Relative humidity — a ratio of how much water vapor is in the air to how much it could contain at a given temperature. Sometimes, the humidity is so high you feel like you could make use of the density calculator.

Remember that both temperature and wet bulb temperature in this formula are expressed in °C! If you would like to use other units, you need to convert them to the Celsius scale before you start calculations.

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.

You may find useful here:

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:

$\footnotesize WBGT = 0.7 T_\mathrm w + 0.2 T_\mathrm g + 0.1 T$

where $\footnotesize T_\mathrm g$ - 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:

$\footnotesize WBGT = 0.7 T_\mathrm w + 0.3 T$

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

FAQs

What is the wet bulb?

A wet bulb is a thermometer in which the bulb is wrapped in a wet cloth. It can be used to measure the lowest temperature to which air can be cooled by evaporating water at constant pressure. Basically, it is a metaphor for human sweat and it will tell you how the human body would feel in direct sunlight.

What is the ideal wet-bulb temperature?

Quite comfortable wet-bulb temperature is around 70 °F (22 °C), but no more than 86 °F (30 °C). Above this temperature, physical labor becomes impossible. The higher the wet-bulb temperature, the higher the risk of severe heat stress.

Is wet-bulb temperature the same as Heat Index?

No. Both Wet-Bulb Globe Temperature (WBGT) and Heat Index measure the human body's ability to resist stress from heat. What they have in common is that they both take into account temperature and relative humidity. The fundamental difference is that WBGT is calculated with temperature measured in the sun, while Heat Index is calculated in the shade. Also, WGBT takes into account more parameters.

What will the wet bulb temperature be at 25°C and 40% relative humidity?

16.384 °C. Calculate this in a few steps:

1. Use the formula for wet-bulb temperature:

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.

2. Insert RH% = 40 % and T = 25 °C into equation.

3. Calculate Tw = 16.384 °C.

What are wet bulb temperature and dry bulb temperature?

The dry-bulb temperature is the air temperature measured by regular thermometers. In contrast, the wet-bulb temperature is the degree to which air can be cooled due to the evaporation of water. It is measured by a thermometer wrapped in a water-soaked cloth. The wet-bulb temperature is always lower than the dry-bulb temperature. The combination of the dry-bulb temperature and the wet-bulb temperature gives the state of the humid air.

This wet bulb calculator is designed to help you estimate the wet bulb temperature based on only two pieces of data - the temperature 🌡️ and the relative humidity 💧.